Fin-rays

Fin-ray counts do not vary within or among species of Hypoptopoma, and therefore fin-ray formulae are presented only in the generic account. A Roman numeral designates the thickened and consolidated spinelike first unbranched ray, whereas numbers of branched rays are denoted by Arabic numerals. Hereafter and throughout the text, the first unbranched ray of the fin is referred to as “spine” in accord with convention, although we recognize that siluriforms lack true acanthomorph-like fin spines.

Teeth

Tooth counts were obtained separately for each jaw ramus and determined for the functional row (i.e., subdermal preemergent replacement teeth not included). Gaps in the tooth row resulting from loss of teeth were counted as one or more teeth present depending on the size of the gap relative to the average tooth width. Given the lack of significant differences between left and right counts, only the right-side tooth count of the premaxilla and dentary are included in the tables.

Plates

Bilateral counts of dermal plates follow Schaefer (1997). Loricariids have five overlapping rows of plates along the trunk (fig. 1). These rows are serially homologous and individual rows are distinguished based on positional relationships to one another and to the trunk lateral-line canal. The medial series, like that in most other hypoptopomines, bears the lateral-line canal; the first medial-series plate is the anteriormost plate in contact with the second midventral plate. Lanceolate plates at the base of the caudal-fin rays were not included in the counts. Given the lack of significant differences between right- and left-side counts, only the right-side series of plate counts are included in the tables.

Fig. 1

Dermal plates of the lateral trunk and serial plate homology. A, Hypoptopoma psilogaster ANSP 138871; B, H. inexspectatum ILPLA 269.

Diagnosis

Distinguished from all other loricariids by having the nuchal plate laterally expanded to such an extent that the distance between distal tips is at least twice the width of the base of the dorsal spine at its widest point (fig. 3B–C). In members of the Loricariinae and Hypoptopomatinae except Niobichthys and Acestridium, the nuchal plate is round to polyhedral, its width equal or slightly surpassing that of the base of the pectoral spine (fig. 3A). In Niobichthys, and members of the Ancistrinae and Hypostomatinae, there is a pair of nuchal plates in contact in the midline. Species of Acestridium possess 2–4 median unpaired predorsal plates (Reis and Lehman, 2009).

Fig. 3

Schematic diagram of the nuchal plate, dorsal view. A, Oxyropsis acutirostra ANSP 164280; B, H. machadoi ANSP 134438; and C, Hypoptopoma baileyi AMNH 39768. Scale bar  =  2 mm.

Hypoptopoma can also be distinguished from all other loricariids, except the hypoptopomatin genus Oxyropsis, by the shape of the head, which is depressed, and by the ventrolateral placement of the eyes. This typical “Hypoptopoma” head shape is further reflected anatomically by a series of uniquely derived osteological characters (shared with Oxyropsis): the lateral ethmoid laterally elongated; the T-shaped third infraorbital, with its lateral platelike side positioned ventrally on the head (fig. 4); the canal-bearing plate presenting more than three-fourths of its surface area positioned ventrally on the head, and the fourth infraorbital reduced, smaller than the fifth infraorbital (fig. 5) (except in H. spectabile). In other taxa, the position of the eyes is lateral to dorsolateral and not visible from below. Accordingly, the lateral ethmoid is not laterally elongated, the third infraorbital is platelike and laterally positioned on the head, the canal-bearing plate presents less than three-fourths of its surface area positioned ventrally on the head, and the fourth infraorbital is larger than the fifth infraorbital.

Fig. 4

Schematic diagram of the ventrolateral aspect of the skull, right side, anterior toward bottom, showing relationship of third infraorbital to lateral ethmoid. A, Hypostomus sp.; B, Hisonotus sp.; and C, Hypoptopoma sp.

Fig. 5

Dermal plates of the head, ventral view: A, H. inexspectatum INPA 269; B, H. steindachneri INHS 40171, and C, H. elongatum INPA 7240.

Hypoptopoma is distinguished from all other Hypoptopomatini, including Oxyropsis, by the shape of the caudal peduncle. The cross section of the trunk posterior to the base of the anal fin is distinctly ovoid, with the dorsoventral axis as the longest. The ovoid shape is enhanced by the uniform size of the odontodes in longitudinal rows across the trunk and, in adults of the largest species in average size, by the smoothness of the plates. Oxyropsis, Acestridium, and Niobichthys possess a narrow and depressed caudal peduncle. The trunk cross section posterior to the base of the anal fin is roughly rectangular to oblate spheroidal in shape, with the horizontal axis as the longest. The lateral edges are enhanced by rows of variably enlarged odontodes, which in Oxyropsis form a keellike ridge in cross section (Aquino and Schaefer, 2002). In Otocinclus, which possess a robust caudal peduncle and the dorsoventral axis the longest, the cross section of the caudal peduncle is progressively rectangular in shape toward the caudal fin (Schaefer, 1997). The rectangular shape is further enhanced by rows of variably enlarged odontodes along the dorsolateral edges of the peduncle.

Hypoptopoma, except for H. spectabile, can be further distinguished among loricariids by the presence of a column of odontodes positioned along the posterior margin of the trunk plates (hereafter termed “marginal odontodes”; fig. 6). The marginal odontodes are not visible in the juvenile stages, becoming progressively conspicuous in ontogeny. Their development takes place with a progressive smoothening of the plate surfaces (in the largest specimens, the plates are smooth, the odontodes reduced in number, and their distribution is restricted to the posterior portion of the plate surface). The marginal odontodes are slightly larger and flattened relative to the typical conical odontodes.

Fig. 6

Photograph of marginal odontodes, left side of trunk between dorsal and adipose fins, anterior toward left. A, H. incognitum, lamina of trunk plates smooth, marginal odontodes well developed; B, Otocinclus flexilis, AMNH 79372, lamina of trunk plates with longitudinal lines of small odontodes, marginal odontodes not markedly developed. Scale bar  =  2 mm.

Description

Adult body size moderately small relative to most other loricariids; maximum size of Hypoptopoma species ranging from 18 to 105 mm SL, attaining greatest body length among genera of Hypoptopomatinae. Head and body almost entirely covered by bony dermal plates, except for area surrounding lips and base of pectoral, pelvic, dorsal, and anal fins. Dermal bones exposed on head and pectoral girdle, and fin rays covered by dermal teeth or odontodes (Bhatti, 1938). Odontodes rather evenly distributed on head, slightly enlarged and variably aligned in dorsal and ventral series on rostral margin of snout, and typically arranged in well-defined longitudinal series on trunk plates. Distinct column of slightly enlarged and flattened marginal odontodes arranged along posterior margin of trunk plates. Anterior surface of pectoral-fin spine and ventral surface of pelvic-fin spine with enlarged odontodes. Series of smaller, irregularly shaped pararostral plates present anterior to each nasal plate between mesethmoid and lateral rostral plates (first to third canal-bearing infraorbitals) and adjacent to naris between nasal plate and lateral rostral plates (fig. 7A). In some species, one or more paranasal plates can be present (one in H. gulare and H. machadoi; two or more in H. steindachneri) (fig. 7B–C).

Fig. 7

Schematic drawing of head, showing topology of dermal plates, dorsal view, right side, anterior toward top. A, H. inexspectatum ILPLA 269; B, H. machadoi CAS 64283; and C, H. steindachneri INHS 40171.

Dorsal-fin rays I,7; anal-fin rays i,5; pectoral-fin rays I,6; pelvic-fin rays i,5; caudal-fin rays i,7-7,i. Adipose fin variably present. Premaxillary teeth 10–36; dentary teeth 10–37. Oral disk rounded, surface papillose and with scattered unculi.

Dermal plates on trunk arranged in five longitudinal, serially homologous rows (fig. 1). Lateral line complete and continuous; total lateral plates (medial series) 20–26; dorsal series 17–22; middorsal series 3–5; midventral series 11–15; ventral series 17–22. Number of midventral series plates between posterior process of cleithrum and first plate of ventral series (roughly triangular plate at base of pelvic-fin spine) three (H. bianale, H. elongatum, H. gulare, H. incognitum, H. inexspectatum, H. machadoi, H. spectabile, H. sternoptychum) (figs. 1B, 8B) or four (H. baileyi, H. brevirostratum H. guianense, H. muzuspi, H. psilogaster, and H. thoracatum) (figs. 1A, 8A), rarely five. Second plate of midventral series contacting a single plate (H. bianale, H. elongatum, H. gulare, H. incognitum, H. inexspectatum, H. machadoi, H. spectabile, H. sternoptychum) (figs. 1B, 8B) or two plates of medial series (H. baileyi, H. brevirostratum H. guianense, H. muzuspi, H. psilogaster, and H. thoracatum) (figs. 1A, 8A). Abdominal plates arranged according to three main patterns: (1) plates arranged in paired series of lateral sickle-shaped plates and medial series of roughly squared plates, each series composed of more than three plates (H. baileyi, H. brevirostratum, H. guianense, H. muzuspi, H. psilogaster, and H. thoracatum) (fig. 9A); (2) plates arranged in paired series of lateral sickle-shaped plates and only one roughly triangular medial plate between anteriormost pair of lateral plates (all other species, except H. spectabilis and H. sternoptychum) (fig. 9B–C), and (3) presence of a pair of slender plates posterior to the coracoids, followed by a series of 1–3 unpaired abdominal plates anterior to the anal plate (H. spectabilis and H. sternoptychum) (Schaefer, 1996a: fig. 1). Thoracic plates present or absent (H. baileyi, H. brevirostratum, H. guianense, H. muzuspi, H. psilogaster, H. spectabilis, and H. thoracatum); when present, forming shield between left and right ventral canal-bearing plates (fig. 9B–C). Anal plate composed of single plate (fig. 9A–B), except in H. bianale, whose shield is two plates (fig. 9C). Fully developed anal plate shaped as blunt, posteriorly oriented arrowhead.

Fig. 8

Anteriormost plates of the canal-bearing medial trunk dermal plate series (shaded), left side, anterior toward left. A, Hypoptopoma thoracatum INHS 40172; and B, H. inexspectatum ILPLA 269.

Fig. 9

Ventral view of abdominal region, anterior toward top, showing relationship of abdominal plate series and anal plates. A, H. thoracatum USNM 308312; B, H. gulare NRM 16561; and C, H. bianale FMNH 117745.

Complete development of lateral series of trunk plates achieved ontogenetically before full development of abdominal shield and plates anterior to naris (fig. 10). Development of trunk-plate series progresses in rostral direction, with individual plates nearest caudal fin developing first. Plates of medial series and bony canals of lateral line develop asynchronously, with lateralis canal ossifying prior to ossification of surrounding plate lamina. Platelike connecting bone (sensu Schaefer, 1987), counted as second middorsal plate, develops prior to plates lying immediately anterior and posterior to middorsal series. Development of abdominal plates initiates with lateral series in an approximately lateral to medial direction. Fully developed individuals can be recognized by having ventral region between pectoral fins entirely covered by abdominal plates.

Fig. 10

Ontogeny of the trunk lateral dermal plate series in Hypoptopoma inexspectatum, UMMZ 205878, showing changes in the pattern, size, and arrangement of plates with growth. Individual plates shown at right depict size and configuration of odontodes relative to plate margins and laterosensory canal. A, 18.6 mm SL; B, 24.3 mm SL; C, 29.0 mm SL; and D, 35.7 mm SL.

Sexual Dimorphism

Male urogenital papilla pointed, short, variably slender, more or less covered by anterior flaplike anus. Males of some species with patch of tightly arranged small odontodes positioned lateral to urogenital papilla and anus, variably developed on plates 1–4 of ventral trunk series. In some species, males with variably developed fringe of soft tissue along posterior margin of pelvic-fin spine, proximal to first branched ray when developed, typically restricted to basal one-third to one-half of spine length. Anus of females tubular, without separate urogenital papilla. In females of all species, size and arrangement of odontodes on plates lateral to anus similar to adjacent plates, without distinct patch of differentially arranged odontodes.

Distribution

Widely distributed in lowland cis-Andean South America, with representatives in the major tributaries of the Amazon, Orinoco, Essequibo, Nickerie, Tocantins, and Paraguay/Paraná rivers (fig. 11).

Fig. 11

Drainage map of South America and distribution of the genus Hypoptopoma. Symbols may represent more than one locality record.

Comparisons

The pattern of odontode distribution on the trunk plates changes during ontogeny. In the smallest specimens of each species, odontodes on the plate lamina have a relatively dense and regular distribution in multiple longitudinal rows, a condition observed widely among species of Loricariidae. In larger specimens (actual size of specimen depends on the species), the distribution of odontodes is more uneven and irregular over the plate surface, resulting in one or more relatively open areas lacking odontodes and giving the plate surface a smoother appearance. A pattern of increased irregularity in odontode distribution and greater proportion of the plate surface without odontodes is correlated with increase in the size of specimens. It has not been determined whether trunk-plate smoothing is due to actual loss of odontodes or plate growth in surface area without corresponding increase in number of odontodes, thus expanding the space among odontodes. Observation of open “sockets,” or alveoli, would suggest both odontode loss and surface ossification as responsible for plate smoothing during ontogeny. Although odontode loss would not be uncommon among loricariids, progressive plate smoothing has not been reported. Among Hypoptopoma species, the greatest degree of plate smoothing is observed mostly among species of the clade at node 7 (see fig. 45) and the largest specimens of H. thoracatum and H. psilogaster. Among non-loricariid loricarioids, some callichthyids have odontodes arranged along the posterior margin of the trunk plates. However notable differences in morphology of individual odontodes and in arrangement of odontodes suggest nonhomology with the condition observed among Hypoptopoma species.

Within the Hypoptopomatinae, Hypoptopoma is most similar to Oxyropsis in external appearance. Representatives of these two genera share the depressed head and the ventrolateral position of eyes (Schaefer, 1997). In addition to the unique presence of the laterally expanded nuchal plate and marginal trunk-plate odontodes, Hypoptopoma can be further distinguished from Oxyropsis by having a trunk ovoid in cross section, the ratio of the caudal-peduncle depth in the caudal-peduncle width >1 (vs. cross section of trunk depressed, rectangular to oblate spheroid shaped in cross section, ratio of caudal-peduncle depth in caudal-peduncle width <1), and by the absence of the single row of enlarged odontodes along the trunk midline lying adjacent and immediately dorsal to the lateral-line canal, a derived character state unique for Oxyropsis (Aquino and Schaefer, 2002).

Taxonomic Remarks

Günther (1868a) distinguished Hypoptopoma by characteristics related to the head: head depressed and spatulate, with the eyes located on the lateral margins of the head. Following this diagnosis, Steindachner (1879) assigned his new species carinatum to the genus Hypoptopoma. Aquino and Schaefer (2002) provided evidence in support of Oxyropsis monophyly and demonstrated that the characteristics used by Günther to distinguish Hypoptopoma are shared with Oxyropsis. A phylogenetic diagnosis of Hypoptopoma (Schaefer, 1991) distinguished the genus on the basis of two osteological characters: (1) canal in the preopercle forming a semicircle, and (2) preopercular canal passing through the fifth infraorbital before entering the preopercle. The present study shows that those two characters are not shared by all species of Hypoptopoma. In a revised analysis, Schaefer (1998) recognized four derived unreversed characters supporting the Hypoptopoma clade (Schaefer, 1998: fig. 3): (1) sphenotic with expanded anterior lamina, (2) preopercle canal semicircular, (3) presence of notch on canal-bearing ventral plate, and (4) trunk plates with enlarged odontodes concentrated along posterior margin (in this paper, marginal odontodes). Likewise, the present study shows that character (1) is shared with other genera of the tribe, and characters (2), (3), and (4) are not shared by all species of Hypoptopoma.

Neurocranium

Mesethmoid long and slender; anterior tip laterally extended (Aquino and Miquelarena, 2000: fig. 5). Ventral process of mesethmoid disk shaped, not terminal (Schaefer, 1991). Nasal approximately triangular in shape (fig. 7). Orbit occupies distinctly lateral position, in correlation with lateral elongation of lateral process of lateral ethmoid. In adults of species of Hypoptopoma gulare group, position of orbits slightly lateroventral, so that dorsal interorbital distance can be greater than ventral interorbital distance.

In dorsal view, supraoccipital large and nearly hexagonal in shape; in ventral view, suturing with neural spines of Weberian complex and expanded neural spine of sixth vertebra (Aquino and Miquelarena, 2000: figs. 7, 17). Frontal and sphenotic bones generally forming dorsal wall of orbital chamber. Sphenotic approximately rectangular in shape. Dorsal rim of orbit formed by fifth infraorbital, sphenotic, frontal, and preorbital plate. Species of the clade at node 6 (see fig. 45) with decreasing contribution of frontal and sphenotic to dorsal rim of orbit with increasing size of individuals (fig. 12); only preorbital plate and fifth infraorbital forming dorsal rim of orbit in largest specimens.

Fig. 12

Schematic diagram of the dorsolateral aspects of the head of Hypoptopoma showing ontogenetic changes in the degree of contribution of the bones to the dorsal rim of the orbit, H. gulare, INHS 39348. A, 52.9 mm SL; B, 62.0 mm SL; and C, 64.0 mm SL; D, 75.0 mm SL.

Compound pterotic enclosing bony capsule of swimbladder anteriorly and dorsally (Aquino and Miquelarena, 2000: fig. 7), with uniformly circular small pores in dorsal view. Lateral ethmoid with pronounced lateral process; laminar expansion of lateral ethmoid partially encapsulating nasal organ from below; anterior process of lateral ethmoid articulating with palatine (Aquino and Miquelarena, 2000: fig. 6). Lateral processes of parasphenoid approximately rectangular in shape, suturing with prootics anteromedially, and interdigitating with median projection and paired shorter lateral processes of basioccipital posteriorly (Aquino and Miquelarena, 2000: fig. 5). Anterior margin of prootic partially bounding compound foramen for trigeminofacialis and optic nerves. Functional posterior myodome formed by one camera limited by prootics, parasphenoid, and basioccipital (Aquino, 1998; Aquino and Miquelarena, 2000: fig. 8b). Posterior wall of lateral process of lateral ethmoid with ridge that serves as insertion point of obliquus eye muscles (Aquino and Miquelarena, 2000: fig. 8a). Exoccipital forming part of anterior wall of swimbladder.

Infraorbital series and laterosensory canals

Infraorbital series composed of five elements. First and second infraorbitals platelike, located lateroposterior to snout rostral plate. Third infraorbital T-shaped, with anterior and posterior limbs platelike and mesial strutlike projection articulating with lateral process of lateral ethmoid (fig. 4). In contrast, third infraorbital platelike in other loricariids. Fourth infraorbital narrow, smaller than fifth infraorbital. Fifth infraorbital with infraorbital canal only (H. baileyi, H. guianense, H. psilogaster, and H. thoracatum) (fig. 13A), or fifth infraorbital with branches from both preoperculo-mandibular canal and infraorbital canal (fig. 13B).

Fig. 13

Third through fifth infraorbital plates, infraorbital canal, canal in preopercle, and ventral canal-bearing plate, left side, anterior toward left. A, Hypoptopoma baileyi UMMZ 205171; B, H. muzuspi MZUSP 95186; C, photograph showing and eyelash passed through the semicircular preopercular laterosensory canal in H. gulare, MCNG 240798. Entrance and exit pores denoted by arrows in B, C. References: io, infraorbital.

Suspensorium and mandibular arch

Hyomandibula largely enclosing orbit from below, articulating with compound pterotic posteriorly, contacting prootic dorsally, and suturing loosely to metapterygoid via bony interdigitations anterodorsally (Aquino and Miquelarena, 2000: fig. 10a–b). Hyomandibula connecting to quadrate via hyosymplectic cartilage anteriorly. Hyomandibula partially overlapping canal-bearing region of preopercle ventrally in species of the clade at node 6 (fig. 14B).

Fig. 14

Preopercle and adjoining bones, right side, lateral view: A, H. baileyi AMNH 243579; B, H. gulare USNM 284866; and C, H. muzuspi 243578.

Metapterygoid approximately trapezoid in shape (Aquino and Miquelarena, 2000: fig. 10a–b). Anterior tip of metapterygoid short and pointed, connecting to three fingerlike processes of palatine that serves as insertion site for extensor tentaculi. Depth of metapterygoid canal less than 50% of its length. Canal extended along first third of dorsal margin of metapterygoid in H. baileyi, H. guianense, H. psilogaster, and H. thoracatum; extended just beyond anterior first half of dorsal margin in other species. Canal elongate and narrow, shelflike lateral lamina narrower than on opposite side in H. baileyi, H. guianense, H. psilogaster, and H. thoracatum; canal widely open, lateral shelflike extension wider than opposite side in other species.

Opercular series

Opercle approximately polygonal in shape (fig. 14), with broad concave area for articulation with hyomandibula. Ridge that serves for insertion of levator operculi largely extending between anteroventral and posterior margins of opercle.

Preopercle not exposed, posterior ramus not reaching hyomandibula adductor crest. Two conditions are recognized: (1) posterior ramus not reaching hyomandibula adductor crest and not reaching to base of opercle condyle, approaching or slightly surpassing tip of opercle (for less than one-third of longest axis of opercle) (fig. 14A) (H. baileyi, H. guianense, H. psilogaster, and H. thoracatum; shared with Otocinclus and Oxyropsis); (2) posterior ramus of preopercle reaching to or reaching base of opercle condyle (approximately at vertical through one-third of longest axis opercle) (fig. 14B–C). Canal in the preopercle present or absent (fig. 14A–C; when present, canal in preopercle semicircular (nearly U-shaped), receiving branch from fifth infraorbital.

Weberian apparatus and axial skeleton

Bony swimbladder capsule elongate laterally and slightly tubular in shape, with small lateral openings covered by skin (Aquino and Miquelarena, 2000: figs. 5, 7). Scaphium discoidal, concave mesially; tripus curving at approximately one-third from anterior tip, with small mesial process connecting via connective tissue with dorsoanterior portion of centrum of Weberian complex (Aquino and Miquelarena, 2000: fig. 16a–b).

Total vertebrae 25–28, inclusive of five vertebrae incorporated into Weberian complex and fused with skull, and single centrum incorporated into ural complex. Two bifid hemal spines (three in other loricariids and most Hypoptopomatinae). Neural spine of sixth vertebra expanded dorsally, suturing to supraoccipital (Aquino and Miquelarena, 2000: fig. 17). Rib of sixth vertebra elongate; tip expanded, contacting dermal plates and connecting bone between rib and transverse process of second dorsal-fin pterygiophore. Seventh vertebra with pair of anterior processes; neural spine not expanded dorsally, contacting distal end of first two pterygiophores of dorsal fin. Expanded lamina of single supraneural bone with pair of anterior processes; supraneural bone suturing with anterior margin of first pterygiophore posteriorly. Ossified pleural ribs posterior to rib of sixth centrum present in H. baileyi, H. guianense, H. psilogaster, H. spectabile, H. sternoptychum, and H. thoracatum. Ribs (except for first and, less often, posteriormost one) with single articulation to anteroventral area of centra via strong connective tissue. Anteriormost rib (and, less often, posteriormost one) typically reduced to ossified “floating” segment of rib connected to centrum via connective tissue at exactly same point where more developed ribs articulate with centrum. Development of ribs, thus length, also varies between left and right sides of body.

Median fins

Caudal skeleton fused into ural complex (Lundberg and Baskin, 1969; Aquino and Miquelarena, 2000: fig. 18a–b). Basipteryigium fenestrae present, except in H. spectabile and H. sternoptychum (Schaefer, 1996a). Caudal-fin myology corresponds with condition described for the Loricariidae (Lundberg and Baskin, 1969; Aquino and Miquelarena, 2000: fig. 19a–b). Fossa muscularis of basipterygium with ventral transverse ridge that serves as insertion point for adductor profundus; transverse ridge orthogonal (vs. ridge oblique in most loricariids) to longitudinal axis of girdle (Aquino and Miquelarena, 2000: fig. 23a).

First dorsal-fin spine (spinelet) and dorsal-fin spine locking mechanism absent. Eight dorsal-fin pterygiophores; transverse processes on second pterygiophore extended, processes of more posterior pterygiophores shorter; last pair of processes forming posterior bifid process. Seven dorsal-fin distal radials, each with short lateral processes. Adipose fin variably present; when present also variable in shape, varying from a patch of odontodes closely arranged to a spiny axis covered by small odontodes supporting a delicate membrane. Six anal-fin pterygiophores; anterior margin of first pterygiophore expanded laterally and connected to anal plate via connective tissue.

Paired fins

Posterior side of pectoral spine serrated, (all species except H. spectabile and H. sternoptychum). When present, serrae showing either oblique (H. baileyi, H. guianense, H. psilogaster, and H. thoracatum) or orthogonal orientation (all other species). Oblique type (fig. 15A–B) characterized by individual serrae oriented at oblique angle relative to pectoral spine axis; tips of individual serrae acute; serrae extend from near distal tip to base of spine, except for short proximal region; serrae well developed throughout ontogeny. Orthogonal type (fig. 15C–D) characterized by individual serrae oriented orthogonal to pectoral spine axis; tips of individual serrae slightly blunt; serrae most prominent along middle region of spine shaft; serrae poorly developed or absent in largest specimens of species with longest average standard length (i.e., H. steindachneri). Two conditions were recognized relative to pectoral-fin radials: (1) three separate radials (H. baileyi, H. guianense, H. psilogaster, and H. thoracatum); and (2) first radial separate, second and third radials sutured along longest axis, suture line variably visible (all other species) (Aquino and Miquelarena, 2000: fig. 22c–d).

Fig. 15

Pectoral-fin spine, right side dorsal view, anterior toward top. A, B, serrae of oblique type, lateral view of whole spine and detail, respectively; C, D, serrae of orthogonal type, lateral view of whole spine and detail, respectively.

Fig. 16

Rostral dermal plates in Hypoptopoma inexspectatum ANSP 175350; frontal view.

Fig. 17

Pigmentation pattern of the caudal fin: A, H. thoracatum; B. H. psilogaster; C, H. guianense; D, H. gulare; E, H. steindachneri; F, H. elongatum; G, H. machadoi.

Fig. 18

Hypoptopoma baileyi, holotype, AMNH 39828, 38.9 mm SL female, in dorsal, lateral, and ventral views.

TABLE 1

Morphometric and Meristic Data for Hypoptopoma baileyi Holotype: AMNH 39828. Paratype: AMNH 243579.

Holotype

AMNH 39828 (♀, 38.9 mm SL) Bolivia: Beni, backwater, Río Itenez, 10 km SE Costa Marques, Brazil; collected by R.M. Bailey and R. Ramos, 10 September 1964.

Paratypes (collected with holotype)

AMNH 243579 (61 ♀ + 18 ♂, 27.5–44.0 mm SL). UMMZ 205171 (75 ♀ + 32 ♂, 6 cs, 27.7–40.6 mm SL).

Other Material Examined

Bolivia, Beni: AMNH 39764 (1 ♀, 25.5 mm SL) Río Itenez, 3 km SE Costa Marques, Brazil; AMNH 39788 (8 ♀ + 1 ♂, 3 cs, 26.6–33.9 mm SL) Río Itenez, 9 km SE Costa Marques, Brazil; AMNH 39841 (4 ♀, 27.7–32.9 mm SL) Oxbow Río Itenez, 9 km SE Costa Marques, Brazil; AMNH 39861 (27 ♀ + 7 ♂, 24.9–41.5 mm SL) Río Itenez, 9 km SE Costa Marques, Brazil; SIUC 30815 (12 ♀, 29.7–35.4 mm SL) Río Matos in Estación Biológica del Beni (bridge nearest entrance, 6 km E of EBB on road to San Ignacio). Santa Cruz: AMNH 229206 (2 ♀, 29.7–31.8 mm SL) Noel Kempff Mercado Nacional Park, Río Paucerna, about 500 m upstream from mouth at Río Itenez; AMNH 229310 (2 ♀, 28.5–33.3 mm SL) Noel Kempff Mercado Nacional Park, Río Itenez, Bahía Piuba at mouth; AMNH 229353 (17 ♀ + 2 ♂, 25.1–37.6 mm SL) Noel Kempff Mercado Nacional Park, Río Itenez, beach about 200 m upstream from Bahía Agua Blanca; CBF 2859 (1 ♀ + 1 ♂, 33.7–43.7 mm SL) Guarayos, Perseverancia, Río Negro.

Diagnosis

Hypoptopoma baileyi is distinguished from all congeners except H. muzuspi by having trunk pigmentation in the form of a lateral band that is progressively darker along medial, midventral, and ventral series of plates, and a caudal-fin pigmentation pattern formed by 6–8 narrow dark brown bars and a dark spot at the base of the lower lobe. Hypoptopoma baileyi is distinguished from H. muzuspi by having preopercle reduced, not reaching hyomandibular-opercle condyle (vs. preopercle not reduced, reaching to hyomandibular-opercle condyle) and absence of canal in preopercle (vs. presence of canal in the preopercle) (fig. 14A).

Description

Morphometric and meristic data presented in table 1. Body size relatively small, moderately elongate, and depressed; greatest body depth at dorsal-fin origin. Dorsal profile of head and body from tip of snout to dorsal-fin origin straight, slightly angled dorsally at anterior supraoccipital tip; straight from dorsal-fin origin to anteriormost procurrent caudal-fin ray. Head moderately depressed, almost as wide as cleithral width; lateral process of lateral ethmoid dorsally not visible. Snout slightly rounded in dorsal view, concave at region anterior to naris. Posterior surface of bony pit of nasal organ gradually inclined. Body cross section between pectoral- and pelvic-fin origins ovoid to transversely depressed, progressively compressed posterior to anal-fin base.

Eyes moderately large, positioned slightly closer to posterior tip of compound pterotic than to tip of snout. Ventral margin of orbit located close to ventral surface of head. Dorsal interorbital distance shorter than ventral interorbital distance.

Total plates in lateral medial series 22–23 (23). Dorsal series 19–21 (20); middorsal series 3–4 (4); midventral series 12–14 (13), with four plates anterior of first plate of ventral series; ventral series 19–21 (20). Second plate of midventral series contacting single plate of medial series.

Abdomen covered by paired series of lateral sickle-shaped plates, with unequal number of plates between left and right side series, 3–9 each; medial series of 3–8 (6) roughly squared plates; anterior azygous plate absent; medial series occasionally absent, in which case paired series make contact along midline in fully developed individuals. Single anal plate present. Thoracic plates absent. Preopercular canal absent. Posterolateral margin of canal-bearing plate and lateral margin of fourth infraorbital smooth; pore between canal-bearing ventral plate and fourth infraorbital absent.

Small odontodes evenly distributed on head, roughly arranged in closely spaced longitudinal lines. Odontodes ventral to tip of snout slightly enlarged. Lamina of trunk plates with longitudinal rows of odontodes, becoming progressively smoother ontogenetically; largest specimens maintain longitudinal rows dorsal to lateral-line canal, rows otherwise absent; distinct column of marginal odontodes on posterior plate border in mature adults.

Total vertebrae 27–28; ribs present. Premaxillary teeth 14–22; dentary teeth 11–18. Maxillary barbels short, not reaching to anterior margin of ventral canal-bearing plate.

Dorsal-fin origin located slightly posterior of vertical through pelvic-fin origin. Depressed dorsal fin reaching to vertical through midpoint of anal-fin length. Pectoral fin reaching to vertical through midpoint along pelvic-fin spine. Depressed pelvic fin close or reaching to plate anterior to anal-fin spine. Extension of serrae along length of pectoral-spine margin, except for short basal segment; serrae of oblique type. Pelvic fin short, unbranched slightly shorter than first branched rays. Depressed fin reaching to anus, not reaching to insertion of anal-fin spine. Caudal fin forked. Adipose fin absent.

Color in alcohol

Ground color tan to pale ochre. Melanophores light to dark brown on trunk and particularly clustered at base of plates resulting in mottled appearance. Melanophores slightly more concentrated on compound pterotic dorsal to swimbladder capsule, anterior half of supraoccipital, frontals, plate anterior to naris, lateral rostral plates on snout, on posterior half of lip surface, band on maxillary barbel, anterior half of branchiostegal membrane, and posterior tip of naris flap. Melanophores scattered or absent on dorsal surface of mesethmoid, anterior rostral plate, and narrow band anterior to epiphysial branch of supraorbital canal in frontal. Deep-lying melanophores arranged in narrow transverse bands posterior to dorsal-fin base, noncoincident with posterior margin of plates. Midlateral stripe situtated along medial, midventral, and ventral series of plates, progressively less pigmented toward ventral surface of body, which is mostly unpigmented except for scattered melanophores on posterior portion of trunk, soft tissue along base of pectoral and anal fins, anterolateral margin of cleithra and posterior tip of cleithral process, ventral canal-bearing plate, and lateral portions of lateral abdominal series. Paired and unpaired fins with relatively numerous narrow dark brown bands. Series of lanceolate plates at base of caudal fin and small posteriormost plate of trunk medial series more densely pigmented with black melanophores. Last 1–2 posteriormost plates of dorsal and ventral trunk series less pigmented, whitish. Upper and lower marginal and branched rays of caudal-fin with 7–10 bands of brown melanophores, with slightly darker area at base of lower lobe.

Sexual dimorphism

Male urogenital papilla elongate, slender papilla covered by flaplike anus. Males with patch of tightly arranged small odontodes on second, third, and fourth plates of ventral series, lateral to urogenital papilla. Female anus tubular, without separate urogenital papilla. In females, size and arrangement of odontodes on plates lateral to anus similar to adjacent plates, without distinct patch of differentially arranged odontodes.

Distribution

Río Iténez, in the upper Rio Madeira basin, along the border between Bolivia and Brazil (fig. 19).

Fig. 19

Drainage map of South America showing distribution of H. baileyi (dots + circle), H. guianense (triangles), and H. psilogaster (squares). Open symbols designate type localities; some symbols represent more than one locality record.

Etymology

The specific epithet baileyi is a patronym honoring Reeve M. Bailey (1911–2000), who collected the specimens of the new species in 1964 during an expedition of the AMNH to the Río Itenez.

Fig. 20

Hypoptopoma guianense, paratype, RMNH 26922, in dorsal, lateral, and ventral views.

TABLE 2

Morphometric and Meristic Data for Hypoptopoma guianense Paratypes: RMNH 26922. Nontypes: AMNH 13666, 220509; BMNH 1983.7.26:12–28; FMNH 69962; INHS 49960.

Holotype

RMNH 26919 (61.5 mm SL) Suriname, left tributary of the Nickerie River, a few kilometers upstream from the Stondansi Falls; collected by H. Boeseman, 30 January 1971 (not seen).

Paratypes

RMNH 26922 (1 ♀ + 3 ♂, 47.0–56.0 mm SL) Suriname, Nickerie River, below Blanche Marie Falls; collected by H. Boeseman, 11 February 1971. USNM 213484 (2 ♀, 48.9–51.6 mm SL) Surinam, left tributary creek upper Nickerie River; collected by H. Boeseman, 30 January 1971.

Other Material Examined

Guyana, Cuyuni-Mazaruni: INHS 49274 (1 ♀, 27.6 mm SL) 1.5 mi. SW Rockstone [Essequibo river]; INHS 49366 (1 juvenile, 29.3 mm SL) 31.9 mi. SSW Rockstone. Potaro-Siparuni: INHS 49402 (1 juvenile, 23.3 mm SL) Essequibo River drainage, Tumatumari Cataract, S bank, below old hydroelectric plant. Upper Demerara-Berbice: AMNH 13341 (2 ♀, 35.5–40.7 mm SL) Malali; AMNH 13666 (1 ♀ + 1 ♂, 38.5–39.2 mm SL) Rockstone, Essequibo River drainage; AMNH 220509 (2 ♀, 46.3–47.5 mm SL) Essequibo River drainage; INHS 49660 (10 ♀ + 2 juveniles, 25.2–63.4 mm SL) Rockstone. Upper Takutu–Upper Essequibo: BMNH 1983.7.26:12–28 (16 ♀ + 1 ♂, 2 cs, 28.5–47.8 mm SL) Rupununi River; BMNH 1983.26:49–54 (6 ♀, 37.2–46.1 mm SL) Rupununi River, Kamarang; FMNH 69962 (3 ♀, 37.3–42.1 mm SL) Moco Moco River.

Diagnosis

Hypoptopoma guianense is distinguished from all congeners by the presence of an elongated dark spot along the median caudal-fin branched rays, involving the lanceolate plates at the base of the fin. The spot is typically extended over an equal number of branched rays of both the upper and lower lobes and along more than two-thirds of the ray length (fig. 17C).

Description

Morphometric and meristic data presented in table 2. Body moderately elongate and low. Dorsal profile of head and body slightly convex from tip of snout to dorsal-fin origin; straight from dorsal-fin origin to anteriormost caudal-fin procurrent ray. Head moderately depressed and narrow. Lateral process of lateral ethmoid dorsally not visible. Snout rounded to slightly spatulate in dorsal view; smoothly rounded in dorsal view; dorsally variably concave anterior to naris. Posterior surface of bony pit of nasal organ sharply inclined. Body cross section between pectoral- and pelvic-fin origins horizontally ovoid, posterior to dorsal fin changing from ovoid to rounded, posterior to adipose-fin base progressively compressed.

Eyes moderately large, positioned closer to posterior tip of compound pterotic than to tip of snout. Ventral margin of orbit located close to ventral surface of head. Dorsal interorbital distance shorter than ventral interorbital distance.

Total plates in lateral medial series 23–24 (23). Dorsal series 20–21 (20); middorsal series 3–4 (4); midventral series 13–15 (13), with four plates (rarely five) anterior of first plate of ventral series; ventral series 19–21 (20). Second plate of midventral series contacting single plate of medial lateral series.

Abdomen covered by paired series of lateral sickle-shaped plates, with unequal number of plates between left and right series, 4–10 each; medial series of 3–8 (5) roughly squared plates; anterior azygous plate absent. Single anal plate present. Thoracic plates absent. Preopercular canal absent. Posterolateral margin of canal-bearing plate and lateral margin of fourth infraorbital smooth; pore between canal-bearing ventral plate and fourth infraorbital absent.

Small odontodes evenly distributed on trunk and head. Odontodes ventral and dorsal to tip of snout not arranged in aligned series. No odontode-free discontinuity between ventral and dorsal odontodes; odontodes dorsal to tip of snout slightly larger than those on head. Lamina of trunk plates with longitudinal lines of odontodes, becoming progressively smoother ontogenetically; distinct column of marginal odontodes on posterior plate border in mature adults.

Total vertebrae 27. Premaxillary teeth 21–26 (23), dentary teeth 17–24 (20). Maxillary barbels short; reaching to anterior margin of ventral canal-bearing plate in adults.

Dorsal-fin origin located slightly posterior of vertical through pelvic-fin origin. Depressed dorsal fin reaching to vertical through midpoint of anal-fin base length. Pectoral fin reaching to vertical through midpoint of pelvic-fin length. Extension of serrae along pectoral spine margin except for short basal segment; serrae of oblique type. Pelvic fin short, 2–3 longest branched rays slightly longer than spine. Depressed fin reaching to plate anterior to anal-fin spine. Caudal-fin margin forked; upper and lower lobes equal and elongate. Adipose fin variably present; when present, minute.

Color in alcohol

Ground color tan and pale ochre. Melanophores dark brown, on trunk and head clustered resulting in mottled appearance; distinct light spot dorsally on each lateral rostral plate. Melanophores slightly more concentrated on anterior surface of lip, along narrow area among compound pterotic, cleithral process and dorsal tip of opercle, at base of dorsal and pectoral fins. Deep-lying melanophores arranged in narrow transverse bands posterior to dorsal-fin base, noncoincident with posterior margin of plates. Midlateral stripe situated along trunk variably defined. Ventral surface of body mostly unpigmented except for scattered melanophores on posterior portion of trunk, soft tissue along base of pectoral and anal fins, anterolateral margin of cleithra, and lateral portions of lateral abdominal series. Paired and dorsal fins with dark brown bars. Caudal-fin bars variable defined (fig. 17C). Presence of elongated dark spot along middle caudal-fin branched rays; spot typically extending over equal number of upper- and lower-lobe rays and along more than two-thirds of ray length; spot connected to lanceolate plates at base of fin. Tip of upper and lower lobes slightly pigmented with reddish-brown melanophores.

Sexual dimorphism

Male urogenital papilla well developed, pointed, joined at base to anterior flaplike anus. Males with patch of tightly arranged small odontodes oriented as a swirl, variably covering first to fourth plates of ventral series, lateral to urogenital papilla. Female anus tubular, without separate urogenital papilla. In females, size and arrangement of odontodes on plates lateral to anus similar to adjacent plates, without distinct patch of differentially arranged odontodes.

Distribution

Known from of the basins of the Essequibo (Guyana) and Nickerie (Surinam) rivers (fig. 19).

Taxonomic Remarks

Prior to the present revision, Hypoptopoma guianense was the only nominal species of Hypoptopoma to be established on the basis of a relatively large number of individuals (approximately 31). The species is most similar to H. psilogaster Fowler, 1915, which has been reported from the Ríos Ampiyacu, Itaya, Nanay, Napo, and Yaguas in Amazonian Peru. Valid taxonomic status of both species is supported on the basis of differences in the caudal-fin pigmentation: both species possess an elongate spot along the middle caudal-fin branched rays, but in H. guianense the spot is continuous with the dark spot on the lanceolate plates, versus discontinous in H. psilogaster. Further differences are shown in an analysis of the overall morphometric variation among H. guianense, H. psilogaster, and H. thoracatum. In a sheared principal component analysis on 18 distance variables (fig. 21; table 3), the scatter plot of the component scores on sheared PC2 and PC3 shows near complete separation among the three species. The second and third components represent 3.1% and 0.9% of the total morphometric variance, respectively. The morphometric variance explained by PC2 reflects differences in the elongation of the body (caudal-peduncle length, trunk length, caudal-peduncle depth); likewise, PC3 appears to reflect differences in head width at the level of the eyes (least distance between orbit and naris).

Fig. 21

Plot of scores along sheared second and third principal components from the morphometric analysis of body shape among H. guianense, H. psilogaster, and H. thoracatum.

TABLE 3

Sheared Principal Component Loadings from the Morphometric Analysis of Head and Trunk of Hypoptopoma guianense, H. psilogaster and H. thoracatum

Fig. 22

Hypoptopoma psilogaster, holotype, ANSP 21922, 51.0 mm SL, juvenile, in dorsal, lateral, and ventral views.

TABLE 4

Morphometric and Meristic Data for Hypoptopoma psilogaster Holotype: ANSP 21922. Nontypes: ANSP 138868; INHS 39826, 44076, 44125; SIUC 23560, 29645.

Holotype

ANSP 21922 (juvenile, 51.0 mm SL) Peruvian Amazon; collected by J. Orton, 1873.

Other Material Examined

Peru, Loreto: ANSP 21921 (1 ♀, 45.6 mm SL) Peruvian Amazon; ANSP 138868 (5 ♀, 33.4–66.5 mm SL) Río Nanay, vicinity of Iquitos, well above Morona Coché (coché 9 m. above Río Amazonas); ANSP 138869 (2; 35.5–39.0 mm SL) Río Nanay, vicinity of Iquitos just above Coché Morona (above 9 m. Río Amazonas); ANSP 138871 (1 ♂ + 3 juveniles, 1 cs, 33.4–66.5 mm SL) Río Nanay, vicinity of Iquitos, Morona Coché outlet (about 9 m. above Río Amazonas); ANSP 178335 (2 ♀, 32.6–41.0 mm SL) Río Itaya at bridge on Iquitos-Nauta highway, approx. 25 miles SSW of Iquitos; CAS 134254 (1 ♀, 32.8 mm SL) Río Ampiyacu; CAS 134255 (1 ♀, 38.1 mm SL) Río Ampiyacu; INHS 39826 (6 ♀, 44.0–70.1 mm SL) Río Nanay, Miz Playa, about 1 hr by canoe upstream from Santa Clara; INHS 44076 (9 ♀ + 2 ♂, 38.9–53.9 mm SL) Río Nanay, Pampa Chica, 4.5 km W center of Iquitos; INHS 44125 (2 ♀, 42.8–48.5 mm SL) Río Napo and Quebrada, Mazán, 33.3 km NE Iquitos; MUSM 7655 (1 ♀ + 1 ♂, 49.7–50.8 mm SL) Río Nanay, Maynas, Iquitos; NRM 18000 (1 ♀, 35.6 mm SL) Río Nanay dr., Caño Puñuisiqui; NRM 47511 (5 ♀, 28.9–35.8 mm SL) Río Nanay dr., small tahuampa cocha on left bank, second left bend above Mishana; SIUC 23560 (83 ♀ + 14 ♂, 5 cs, 28.8–55.9 mm SL) Maynas, Río Nanay at Santa Clara, NW of Iquitos; SIUC 28015 (3 ♀ + 1 ♂, 32.8–48.7 mm SL) Río Nanay at Santa Clara; SIUC 28180 (2 ♀, 35.0–40.2 mm SL) Río Nanay, Pamachica Beach in Iquitos; SIUC 28997 (3 ♀, 29.9–44.0 mm SL) Río Nanay, Miz Playa; SIUC 29489 (1 ♀, 46.5 mm SL) Miz Playa just upstream from Santa Clara, 13.9 km from Iquitos; SIUC 29645 (4 ♀ + 2 ♂, 38.4–56.3 mm SL) Maynas, Río Nanay, Pampachica Beach 4.5 km from Iquitos center; SIUC 67367 (2 ♀, 44.6–51.9 mm SL) Maynas, Río Itaya and Quebrada Mazana, 11 km from Iquitos center; SU 60557 (1 ♀, 41.3 mm SL) Rio Yaguas Yacu; USNM 284882 (2 ♀, 47.3–47.3 mm SL) Río Nanay at Nanay beach, W of Iquitos; USNM 284876 (1 juvenile, 47.2 mm SL) Río Nanay approximately 20 km upstream of mouth; USNM 284883 (2 ♀, 30.7–30.7 mm SL) Río Nanay approximately 20 km upstream of mouth.

Diagnosis

Hypoptopoma psilogaster is distinguished from all congeners by the presence of an elongated dark spot along the middle caudal-fin branched rays, not involving the lanceolate plates at the base of the fin; the spot is typically extended over equal number of upper- and lower-lobe branched rays and along more than two-thirds of the ray length (figs. 17B, 23).

Fig. 23

Hypoptopoma psilogaster, ANSP 180654, 59.2 mm SL, female, in dorsal, lateral, and ventral views.

Description

Morphometric and meristic data presented in table 4. Body elongate, moderately depressed, greatest body depth at dorsal-fin origin, trunk most shallow at caudal peduncle anterior to caudal fin. Dorsal profile of head and body straight from tip of snout to dorsal-fin origin; straight from dorsal-fin origin to anteriormost procurrent caudal-fin ray. Head moderately depressed and narrow; lateral process of lateral ethmoid not visible dorsally. Snout rounded in dorsal view; dorsally smoothly round, slightly concave to flat anterior to naris. Body cross section between pectoral- and pelvic-fin origin horizontally ovoid, vertically ovoid posterior to dorsal fin, progressively compressed posterior to adipose fin.

Eyes moderately large, positioned slightly closer to posterior tip of compound pterotic than to tip of snout. Ventral margin of orbit located close to ventral surface of head. Dorsal interorbital distance shorter than ventral interorbital distance.

Total plates in lateral medial series 24–26 (24); when total plates 25 or 26, posteriormost plate very small, with canal not reaching to posterior border of plate. Dorsal series 20–22 (21); middorsal series 3–4 (4); midventral series 13–14 (13), with 4–5 (4) plates anterior of first plate of ventral series; ventral series 20–22 (21). Second plate of midventral series contacting a single plate of medial lateral series.

Abdomen covered by paired series of lateral sickle-shaped plates, with unequal number of plates between left and right series, 6–10 each; medial series of 6–10 (8) roughly squared plates; anterior azygous plate absent; medial series occasionally absent, in which case paired series make contact along midline in fully developed individuals. Single anal plate present. Thoracic plates absent. Preopercular canal absent. Posterolateral margin of canal-bearing plate and lateral margin of fourth infraorbital smooth; pore between canal-bearing ventral plate and fourth infraorbital absent.

Small odontodes evenly distributed on head. Odontodes ventral and dorsal to tip of snout not arranged in aligned series. No odontode-free discontinuity between ventral and dorsal odontodes; odontodes dorsal to tip of snout slightly larger than those on head. Lamina of trunk plates bearing longitudinal rows of odontodes, plates becoming progressively smoother ontogenetically; distinct column of marginal odontodes on posterior plate border in mature adults.

Total vertebrae 28. Premaxillary teeth 19–26 (22), dentary teeth 16–24 (19). Maxillary barbels short; almost reaching to or slightly surpassing anterior margin of ventral canal-bearing plate in adults.

Dorsal-fin origin located at vertical through pelvic-fin origin. Depressed dorsal fin reaching to vertical through midpoint of anal-fin base. Pectoral fin reaching to vertical through posterior half of pelvic-fin length. Extension of serrae along pectoral spine margin, except for short basal segment; serrae of oblique type; teeth of serrae progressively smaller toward distal end of spine. Pelvic fin short, two longest branched rays slightly longer than spine. Depressed fin reaching to plate anterior to anal-fin spine. Caudal-fin margin forked; upper and lower lobes equal and elongate. Adipose fin present.

Color in alcohol

Ground color tan and pale ochre. Melanophores dark brown, clustered on trunk and head resulting in mottled appearance. Melanophores slightly more concentrated dorsally on head, narrow area among compound pterotic, cleithral process and opercle, and at base of dorsal fin. Deep-lying melanophores slightly more concentrated along midline posterior to dorsal-fin base. Midlateral stripe situated mostly along medial series of trunk plates. Ventral surface of body mostly unpigmented, except for scattered melanophores on soft tissue along base of pectoral-fin branched rays and anterior surface of lip. Paired and dorsal fins with dark brown bands. Black melanophores slightly more concentrated over lanceolate plates. Caudal-fin bars variable defined. Presence of elongated dark spot along middle caudal-fin branched rays; spot typically extending over equal number of upper- and lower-lobe branched rays and along more than two-thirds of ray length; spot not distinctly connected to lanceolate plates at base of fin (fig. 17B). Tip of upper and lower lobes pigmented with dark melanophores.

Sexual dimorphism

Male urogenital papilla short and conical, covered by anterior flaplike anus. Males with patch of tightly arranged small odontodes, variably covering first to fourth plates of ventral series, lateral to urogenital papilla. Males with poorly developed soft-tissue flap along posterior margin of pelvic spine. Female anus tubular, without separate urogenital papilla. In females, size and arrangement of odontodes on plates lateral to anus similar to adjacent plates, without distinct patch of differentially arranged odontodes. Female pelvic spine without flap of soft tissue on posterior surface.

Distribution

Ríos Ampiyacu, Itaya, Nanay, Napo, and Yaguas in Western Amazon (fig. 19).

Taxonomic Remarks

Fowler (1915) established the new species Hypoptopoma psilogaster on the basis of a single specimen. He compared his new species only with H. thoracatum, from which he distinguished the new species by the presence of two rows of abdominal plates separated by an unplated surface (vs. complete cover of the abdominal region with three rows of plates). Our examination of specimens of various size from across an extensive range of the Peruvian Amazon allowed us to confirm that the specimen examined by Fowler possesses the typical arrangement of abdominal plates observed in immature developmental stages in all speces of Hypoptopoma. Adults of H. psilogaster have the abdominal region completely covered by three rows of plates, similar to the condition observed in H. thoracatum. Nevertheless, we provide new evidence supporting the valid taxonomic status of H. psilogaster on the basis of the caudal-fin pigmentation, in addition to a combination of morphometric and meristic characteristics. A multivariate analysis of the overall morphometric variation among H. guianense, H. psilogaster, and H. thoracatum is included in the Taxonomic Remarks section of the systematic account of H. guianense.

TABLE 5

Morphometric and Meristic Data for Hypoptopoma thoracatum Syntype of H. bilobatum: ANSP 8280. Nontypes: AMNH 78033, 78099; CAS 153141; FMNH 101544, 107058, 107059, 107060, 107063, 107069; INHS 101389; LACM 38608; MUSM 1845, 4413; SIUC 29199; SU 36218.

Holotype

BMNH 1867-6:13–38, 76.2 mm SL, Peru, Xeberos.

Non-Types

Bolivia, Beni: INHS 37227 (11 ♀ + 2 ♂ + 1 juvenile, 19.9–42.4 mm SL) Río Apere/Amazonas dr., Río Chevejecure, 41 km E Estación Biológica del Beni on road to San Ignacio; ZSM 28426 (1 ♀, 44.7 mm SL) Espiritu, Río Yacuma. Pando: FMNH 107059 (3 ♂, 42.1–47.8 mm SL) Río Madeira dr., Río Nareuda, 7 km río arriba de la desembocadura en el Tahuamanu; FMNH 107060 (19 ♀ + 2 ♂, 30.2–42.0 mm SL) Río Madeira dr., Río Manuripi, +/− 12 km río arriba de Puerto Rico; FMNH 107061 (7 juveniles, 25.0–29.4 mm SL) Río Madeira dr., lago del campamento, +/− 10 km río arriba de Puerto Rico; FMNH 107063 (2 ♀ + 1 ♂ + 9 juveniles, 30.8–47.2 mm SL) Río Madeira dr., Río Manuripi, +/− 13 km río arriba de Puerto Rico; FMNH 107064 (3 ♀, 28.0–33.1 mm SL) Río Madeira dr., Río Manuripi, +/− 13 km río arriba de Puerto Rico; FMNH 107065 (1 ♀ + 14 juveniles, 25.6–47.1 mm SL) Río Madeira dr., lago s/n, +/− 15 km río arriba de Puerto Rico; FMNH 107066 (9 juveniles, 29.1–33.4 mm SL) Río Madeira dr., lago s/n; +/− 13 km río arriba de Puerto Rico; FMNH 107067 (31 ♀ + 2 ♂, 29.5–40.2 mm SL) Río Madeira dr., lago s/n; +/− 12 km río arriba de Puerto Rico; FMNH 107068 (4 ♀, 32.8–36.6 mm SL) Río Madeira dr., Río Orthon, +/− 2 km río abajo de Puerto Rico; FMNH 107069 (1 ♀ + 1 ♂ + 10 juveniles, 24.1–49.3 mm SL) Río Madeira dr., Río Manuripi; +/− 8 km río arriba de Puerto Rico; FMNH 107070 (3 ♀, 32.4–34.1 mm SL) Río Madeira dr., Río Manuripi at playa, 5.78 km from camp, 9.23 from Puerto Rico; FMNH 107071 (54 juveniles, 26.9–31.9 mm SL) Río Madeira dr., lagoon and backwater off Río Manuripi, 1.70 km above Puerto Rico; FMNH 107072 (4 ♀, 30.8–32.3 mm SL) Río Madeira dr., lagoon on SW side of island 3.47 km up river from Puerto Rico on the Río Manuripi. Brazil, Amazonas: INPA 14036 (8 ♀ + 5 ♂, 41.1–47.4 mm SL) Rio Solimões, Paraná do Rei, Ilha do Careiro; USNM 308312 (1 ♀, 49.9 mm SL) near Manaus, Lago January, Lago Terra Preta; USNM 308336 (1 ♂, 40.3 mm SL) near Manaus, Lago January, Lago Terra Preta; USNM 316539 (7 ♂, 33.3–38.8 mm SL) Rio Purus. Pará: FMNH 59620 (1 ♀, 40.20 mm SL) Santarém. Colombia, Amazonas: CAS 76651 (1 ♀, 46.0 mm SL) Caqueta Dept., Tres Esquinas; CAS 153141 (6 ♀ + 1 ♂, 41.8–73.1 mm SL) Caqueta Dept., Río Orteguaza, tributary of Río Caqueta, within 2 mi. of Tres Esquinas; SU 50479 (4 ♀ + 2 ♂, 36.9–43.9 mm SL) Caqueta Dept., vecinity of Tres Esquinas, Río Orteguaza near juncture with Río Caqueta; USNM 360864 (1 ♀ + 1 ♂, 68.8–75.8 mm SL) Leticia. Ecuador, Napo: FMNH 101544 (3 ♂, 53.2–62.2 mm SL) Tributary to Rio Tarapuy. Peru, Loreto: AMNH 78033 (1 ♀, 55.7 mm SL) Río Tahuayo at Huasi Villeage; AMNH 78099 (9 ♀ + 1 ♂, 1 cs, 45.8–76.9 mm SL) Río Yarapa, tributary of Río Ucayali, several sites along a 10 km stretch of river; AMNH 218005 (1 ♀, 66.4 mm SL) Iquitos, Río Itaya; ANSP 8280/81 (syntypes of Hypoptopoma bilobatum) (2, unsexed, 59.5–74.9 mm SL) Pebas; CAS 59599 (3 ♀, 43.03–48.78 mm SL) mouth of Río Pacaya; CAS 134256 (1 ♀, 46.3 mm SL) Río Ampiyacu; CAS 136219 (1 ♀, 56.5 mm SL) Caño del Chancho, near Pebas; INHS 53870 (8 ♀, 33.0–53.7 mm SL) Río Itaya, Ullpa caño, SE of Belem (Iquitos), near confluence with Moena caño; INHS 101388 (1 ♀ + 1 ♂, 52.3–64.8 mm SL) Río Yanashi, Yanashi, 69.8 mi E Iquitos; INHS 101389 (8 ♀ + 2 ♂, 2 cs, 32.1–73.1 mm SL) Río Orosa, mouth of Tonche Caño, Madre Selva II field station 69.4 mi. E Iquitos; INHS 101391 (1 ♀, 68.6 mm SL) Quebrada Mazama, Río Itaya dr., ca. 1 km upstream from confluence with Río Itaya, S of Belem (Iquitos); MUSM 4413 (3 ♀, 49.7–54.5 mm SL) Alto Amazonas, Yurimaguas, Río Shanusi; MUSM 6515 (1♀, 64.3) Maynas, Puesto de Vigilancia Arcadia, Río Napo, Cocha de Conchas; NRM 17992 (3 ♀, 45.8–48.7 mm SL) Río Samiria drainage, Atún caño; NRM 57232 (1 ♀ + 1 ♂, 54.2–60.9 mm SL) Rio Tahuayo dr., caño Huayti; SIUC 29199 (1 ♀ + 1 ♂, 68.3–78.3 mm SL) Maynas, Río Itaya, upriver of Belén, approx. 4.5 km; SIUC 29316 (1 ♀, 66.6 mm SL) Río Napo, Mazan, 33.3 km from center of Iquitos; SIUC 29782 (1, 54.6 mm SL) Maynas, Río Itaya, 11 km from Iquitos center; SIUC 67366 (5 ♀, 44.6–53.1 mm SL) Maynas, Río Itaya and Quebrada Mazana, 11 km from Iquitos center; SU 36218 (2 ♀, 57.4–67.6 mm SL) Río Amazonas, Caño del Chancho, near Pebas. Ucayali: LACM 38608 (3 unsexed, 47.0–66.6 mm SL) Central Ucayali, brook between Lake Cocha and Lake Yarina; MHNG 2407.98 (1 ♀, 35.3 mm SL) Pucallpa, Tapistica Alejandria; MHNG 2409.26 (1 ♀, 50.6 mm SL) Pucallpa, Masisea, Río Ucayali; MHNG 2409.27 (1 ♀, 41.4 mm SL) Pucallpa, Masisea, Río Ucayali; MHNG 2618.84 (1 ♂, 55.07 mm SL) Río Puntichao and Río Chicosa, two tributaries entering Ucayali River near Chicosa; MHNG 2708.059 (2 ♀, 37.4–38.6 mm SL) Yarina Cocha, an oxbow lake near Pucallpa; MUSM 32157 (3 ♀ + 2 ♂, 1 cs, 43.3–59.6 mm SL) Coronel Portillo, Pucallpa, Tapistica Alejandria; MUSM 32158 (2 ♀, 47.2–50.1 mm SL) Coronel Portillo, Pucallpa, Río Ucayali, Cocha Tacshitea; NRM 17987 (2 ♀, 64.4–64.6 mm SL) Río Ucayali dr., Yarinacocha, caño to Paca Cocha.

Diagnosis

Hypoptopoma thoracatum is distinguished from all congeners by the presence of an elongated spot of black melanophores along the caudal-fin branched rays, not distinctly connected to the lanceolate plates at the base of the fin; spot extended over a larger number of lower-lobe rays than upper-lobe rays and along one-half to more than two-thirds of the ray length (figs. 17A, 24).

Fig. 24

Hypoptopoma thoracatum, SIUC 30062, 54.0 mm SL, female, in dorsal, lateral, and ventral views.

Description

Morphometric and meristic data presented in table 5. Body moderately robust. Dorsal profile of head and body straight from tip of snout to dorsal-fin origin, slightly elevated at predorsal plates; straight from dorsal-fin origin to anteriormost caudal-fin procurrent ray. Head moderately depressed and wide. Lateral process of lateral ethmoid bone visible dorsally. Snout slightly rounded in dorsal view; dorsally smoothly rounded, slightly concave anterior to naris. Posterior surface of bony pit of nasal organ gradually inclined. Body cross section between pectoral- and pelvic-fin origins horizontally ovoid, vertically ovoid to progressively rounded posterior to dorsal fin, progressively compressed posterior to adipose-fin base.

Eyes moderately large, positioned slightly closer to posterior tip of compound pterotic than to tip of snout. Ventral margin of orbit located close to ventral surface of head. Dorsal interorbital distance slightly shorter than ventral interorbital distance.

Total plates in lateral medial series 22–24 (23). Dorsal series 19–21 (20); middorsal series 3–4 (4); midventral series 13–14 (13), with 4–5 (4) plates anterior of first plate of ventral series; ventral series 19–21 (20). Second plate of midventral series contacting a single plate of medial lateral series.

Abdomen covered by paired series of lateral sickle-shaped plates, with unequal number of plates between left and right series, 5–11 each; medial series of 5–13 (8) roughly squared plates; anterior azygous plate absent; occasionally, transversal series of more than three small plates posterior of coracoids, not aligned with main three longitudinal series. Single anal plate present. Thoracic plates absent. Preopercular canal absent. Posterolateral margin of canal-bearing plate and lateral margin of fourth infraorbital smooth; pore between canal-bearing ventral plate and fourth infraorbital absent.

Small odontodes evenly distributed on head. Odontodes ventral and dorsal to tip of snout not arranged in aligned series. No odontode-free discontinuity between ventral and dorsal odontodes; odontodes dorsal to tip of snout slightly larger than those on head. Lamina of trunk plates bearing longitudinal rows of odontodes, and becoming progressively smoother ontogenetically; distinct column of marginal odontodes on posterior plate border in mature adults.

Total vertebrae 27. Premaxillary teeth 19–34 (24); dentary teeth 14–28 (20). Maxillary barbels short, almost reaching to or slightly surpassing anterior margin of ventral canal-bearing plate in adults.

Dorsal-fin origin located slightly posterior of vertical through pelvic-fin origin. Depressed dorsal fin reaching to vertical through posterior half of anal-fin base. Pectoral fin reaching to vertical through midpoint of pelvic-fin base. Extension of serrae along pectoral spine margin, except for short basal segment; serrae of oblique type. Pelvic fin short, two longest branched rays slightly longer than spine. Depressed fin reaching to plate anterior to anal-fin spine. Caudal-fin margin forked; upper and lower lobes equal and not extremely elongate. Adipose fin present.

Color in alcohol

Ground color tan and pale ochre. Melanophores light to dark brown, clustered resulting in mottled appearance. Melanophores slightly more concentrated dorsally on head, narrow area among compound pterotic, cleithral process, and opercle, at base of dorsal fin, anterior surface of lip, and anterior half of branchiostegal membrane. Head uniformly tan dorsally, except for darker area over brain. Deep-lying melanophores arranged in narrow transverse bands posterior to dorsal-fin base, noncoincident with posterior margin of plates. Midlateral stripe situated mostly along medial series of trunk plates (fig. 24). Ventral surface of body mostly unpigmented, except for scattered melanophores on posterior portion of trunk, soft tissue along base of pectoral and anal fins, anterolateral margin of cleithrum and posterior tip of cleithral process, ventral canal-bearing plates, and lateral portions of lateral series of abdominal plates. Dorsal and anal fins with dark brown bands. Caudal-fin bars variable defined. Presence of an elongated spot of black melanophores along caudal-fin branched rays, not distinctly connected to lanceolate plates at base of fin; spot typically extending over larger number of lower-lobe rays than upper-lobe rays and along one-half to more than two-thirds of ray length (figs. 17A, 24). Tip of upper and lower lobes variably dark.

Sexual dimorphism

Male urogenital papilla short and slender, covered by anterior flaplike anus. Males with patch of tightly arranged small odontodes oriented as a swirl, variably covering first to fourth plates of ventral series, lateral to urogenital papilla. Males with flaplike anus along posterior margin of pelvic spine variably developed; when present, short, weakly developed, restricted to basal one-third to half of spine. Female anus tubular, without separate urogenital papilla. In females, size and arrangement of odontodes on plates lateral to anus similar to adjacent plates, without distinct patch of differentially arranged odontodes. Female pelvic spine without flap of soft tissue on posterior surface.

Taxonomic Remarks

The genus Hypoptopoma was established by Günther (1868a) for his new species Hypoptopoma thoracatum (fig. 2) on the basis of one specimen collected by Barlett at Xeberos (Peru, upper Amazon). He distinguished the new taxon from the loricariid Plecostomus [ =  Hypostomus] by the “peculiar formation of the head, depressed, spatulate, the eyes being on the lateral edges of the head.” During 1868, Günther published two papers in which he provided a taxonomic account of the new genus and species. In the first publication, Günther (1868a) provided a brief diagnosis for the genus and the new species H. thoracatum that only specified counts for fin rays and lateral-line plates. A subsequent expanded description of H. thoracatum was published later during the same year (Günther, 1868b). Therefore, H. thoracatum is considered the type species of the genus. Regarding Hypoptopoma bilobatum, Cope (1870) established the new species on the basis of one specimen collected in 1869 by Hauxwell in Pebas, Ecuador (a region which is now part of Peru), but failed to provide a justification for the proposition of a new species distinguishable from H. thoracatum Günther 1868a, the only species described for the genus at the time. Ultimately, Eigenmann and Eigenmann (1889) placed Cope's species as junior synonym of H. thoracatum, a designation that has been maintained in the literature almost invariably since then, and confirmed herein.

Distribution

Ríos Caqueta, Mamoré, Purus, and Ucayali of Western Amazon (fig. 25).

Fig. 25

Drainage map of South America showing distribution of H. thoracatum (dots + circle). The open symbol designates the type locality; some symbols represent more than one locality record.

Fig. 26

Hypoptopoma brevirostratum, holotype, FMNH 105076, 34.0 mm SL, female, in dorsal, lateral, and ventral views.

TABLE 6

Morphometric and Meristic Data for Hypoptopoma brevirostratum Holotype: FMNH 105076. Paratypes: FMNH 117744; AMNH 243577. Nontypes: FMNH 101541; INHS 44126; INPA 14317; SIUC 27969.

Holotype

FMNH 105076 (♀, 34.0 mm SL) Colombia: Rio Amazonas, 1 mi. upstream from Leticia; collected by Navarro, Thomerson et al., 11 November 1973.

Paratypes (collected with holotype)

FMNH 117744 (14 ♀ + 4 ♂, 29.1–39.3 mm SL). AMNH 243577 (1 ♀ + 1 ♂, 33.2–34.0 mm SL).

Non-Types

Brazil, Amazonas: INPA 14317 (11 ♀ + 2 ♂, 2 cs, 24.1–32.1 mm SL) Rio Solimões, 1 km acima do Furo Paracuuba; INPA 14322 (1 ♀, 38.3 mm SL) Ihla Marchantaria. MZUSP 7015 (1 ♀, 28.2 mm SL) Rio Madeira, 25 km abaixo de Nova Olinda; MZUSP 36214 (1 ♀ + 1 ♂, 29.0–44.0 mm SL) Rio Japura, Manacabi, approximatly 50 km from Foz; MZUSP 36221 (4 ♀, 25.5–38.00 mm SL) Braço do Rio Solimões, Ihla Sorubim, acima do Coari; MZUSP 56820 (1 ♀; 30.6 mm SL) Rio Juruá, 10,2 km abaixo do Lago Pauapixuna. Ecuador, Napo: FMNH 101541 (1 ♀ + 3 ♂, 41.0–50.6 mm SL) Río Jivino, lower 4 km (mostly) to ca. 6 km upstream from mouth. Peru, Loreto: INHS 44126 (1 ♀, 48.8 mm SL) Río Napo and Quebrada Mazán, 33.3 km NE Iquitos; ANSP 187332 (1 ♀ + 1 ♂ + 2 juveniles, 29.6–49.0 mm SL) Río Itaya at bridge on Iquitos-Nauta highway, approx. 25 miles SSW of Iquitos; SIUC 27969 (1 ♂, 41.8 mm SL) Río Mazán.

Diagnosis

Hypoptopoma brevirostratum is distinguished from all congeners, with the exception of H. muzuspi, by having the preopercle constricted medially (vs. preopercle with no constriction); canal in preopercle present, semicircular, located posterior to the preopercle constriction (vs. canal absent from preopercle). Hypoptopoma brevirostratum is distinguished from H. muzuspi by its wider body (cleithral width 23.7–27.0 (25.7) vs. 19.1–23.5 (22.2)), a deeper caudal peduncle (caudal-peduncle depth 6.4–9.1 (7.7) vs. 5.2–6.7 (5.8)), and a larger eye (horizontal eye diameter 19.8–23.3 (21.7) vs. 13.6–20.7 (18.4)).

Description

Morphometric and meristic data presented in table 6. Body moderately wide and depressed; greatest depth at dorsal-fin origin. Dorsal profile of head and body, from tip of snout to dorsal-fin origin, smoothly convex to straight; straight posterior to dorsal-fin base. Head moderately depressed, almost as wide as cleithral width; lateral process of lateral ethmoid not visible dorsally. Snout rounded and short in dorsal view; dorsally slightly concave anterior to naris. Posterior surface of bony pit of nasal organ sharply inclined. Body cross section between pectoral- and pelvic-fin origins approximately ovoid horizontally, slightly rectangular posterior to dorsal fin, slightly compressed at level of two posteriormost lateral trunk plates.

Eyes large, positioned equally distant from posterior tip of compound pterotic and to tip of snout. Ventral margin of orbit located on ventral surface of head. Dorsal interorbital distance typically slightly greater than ventral interorbital distance.

Total plates in lateral medial series 23. Dorsal series 19–20 (20); middorsal series 3–4 (3); midventral series, 12–15 (13), with four plates anterior of first plate of ventral series; ventral series 19–20 (20). Second plate of midventral series contacting one plate of medial lateral series.

Abdomen covered by paired series of lateral sickle-shaped plates, with unequal number of plates between left and right series, 3–8; medial series of 1–3 (2) roughly squared plates; medial series occasionally absent, in which case paired series make contact along midline in fully developed individuals; abdominal shield fully developed in specimens greater than 25 mm SL. Single anal plate present. Thoracic plates absent. Canal in the preopercle present, semicircular; anteriormost pore opening between ventral canal-bearing plate and fourth infraorbital; posterolateral margin of canal-bearing plate and lateral margin of fourth infraorbital with notch for pore of semicircular canal poorly defined.

Small odontodes evenly distributed on head. Odontodes ventral and dorsal to tip of snout on anterior rostral plate not arranged in well-defined series. No odontode-free discontinuity between ventral and dorsal odontodes; odontodes dorsal to tip of snout small, slightly larger than those on dorsal surface of head. Odontodes on lamina of trunk plates roughly arranged in longitudinal rows; feeble column of marginal odontodes on posterior border of plates. No visible progressive smoothening of plates ontogenetically.

Total vertebrae 27. Premaxillary teeth 10–28 (19), dentary teeth 12–22 (18). Maxillary barbels short, not reaching to ventral canal-bearing plate in adults.

Dorsal-fin origin located at vertical through pelvic-fin origin. Depressed dorsal fin reaching to vertical through posterior half of anal-fin base. Pectoral fin almost reaching to vertical through tip of longest pelvic-fin ray. Extension of serrae along pectoral spine margin, except for short basal segment; serrae of oblique type. Pelvic fin short, unbranched rays slightly shorter than first branched. Depressed fin reaching to plate anterior to anal-fin spine. Caudal-fin margin slightly forked; upper and lower lobes equal. Adipose fin absent.

Color in alcohol

Ground color tan and pale ochre. Melanophores dark brown, irregularly distributed on trunk resulting in an overall marbled pattern. Melanophores on head not uniformly distributed. Melanophores slightly more concentrated between left and right nares and anterior to each naris, on anterior margin of opercle, cleithral posterior process, lateral rostral plates and anterior surface of lip. Narrow line of dark melanophores along margin of tip of snout. In dorsal view, melanophores arranged in ill-defined darker clusters (one on predorsal plate, two lighter clusters lateral to dorsal-fin base, two or three posterior to dorsal fin). Midlateral stripe fading toward dorsal surface of trunk and toward caudal fin. Ventral surface of body mostly unpigmented. Three to six dark blotches along dorsal-fin spine, weakly extended over branched rays. Basal triangular dark brown to black spot at base of caudal-fin lower lobe; 3–6 dark blotches along caudal-fin unbranched rays, weakly extended over branched rays.

Sexual dimorphism

Male urogenital papilla completely covered by flaplike anus; joined at base. Males with patch of tightly arranged small odontodes oriented as a swirl covering second, third, and fourth plates of ventral series, lateral to urogenital papilla. Males with soft-tissue flap along posterior margin of pelvic spine variably developed; when present, short, restricted to basal one-third to one-half of spine. Female anus tubular, without separate urogenital papilla. In females, size and arrangement of odontodes on plates lateral to anus similar to adjacent plates, without distinct patch of differentially arranged odontodes. Female pelvic spine without flap of soft tissue on posterior surface.

Distribution

Tributaries of Río Amazonas between confluence of Ucayali-Marañon rivers and Manaus (fig. 27).

Fig. 27

Drainage map of South America showing distribution of H. brevirostratum (dots + circle), H. muzuspi (square), H. spectabile (triangles), and H. sternoptychum (stars). Open symbols designate type localities; some symbols represent more than one locality record.

Etymology

The specific epithet brevirostratum (Lt. brevis, meaning “short”; Lt. rostrum, meaning “snout”)is a reference to the short head.

Fig. 28

Hypoptopoma muzuspi, holotype, MZUSP 52135, 36.3 mm SL male, in dorsal, lateral, and ventral views.

TABLE 7

Morphometric and Meristic Data for Hypoptopoma muzuspi Holotype: MZUSP 52135. Paratypes: MZUSP 95186; AMNH 243578.

Holotype

MZUSP 52135 (♂, 36.3 mm SL) Brazil: Tocantins State, Araguaçu, rio Agua Fria, fazenda Praia Alta 2, estrada Araguaçu/Barreira do Piqui, 27 km ao norte de Araguaçu; collected by Lima et al., 6 July 1997.

Paratypes (collected with holotype)

MZUSP 95186 (24 ♀, 2 cs, 19.0–31.0 mm SL). AMNH 243578 (5 ♀, 1 cs, 28.0–32.0 mm SL).

Diagnosis

Hypoptopoma muzuspi is distinguished from all congeners by having the bifid neural spines of vertebra 10–12 expanded distally (vs. bifid neural spines progressively pointed distally). It can be further distinguished from all congeners, except H. brevirostratum, by the preopercle constricted medially (vs. preopercle without constriction) and canal in preopercle present, semicircular, and located posterior to the preopercle constriction. Hypoptopoma muzuspi can be readily distinguished from H. brevirostratum by its more elongated body and head (body depth 13.8–16.7 (14.7) vs. 15.5–19.2 (17.6); cleithral width 19.1–23.5 (22.2), vs. 23.7–27.0 (25.7); caudal-peduncle depth 5.2–6.7 (5.8) vs. 6.4–9.1 (7.7)), and caudal-fin pigmentation comprised of 7–10 bars of brown melanophores on unbranched and branched rays (vs. 3–6 dark blotches along unbranched rays, weakly extended over branched rays).

Description

Morphometric and meristic data presented in table 7. Body moderately elongate; greatest depth at dorsal-fin origin, trunk most shallow at origin of caudal-fin procurrent rays. Dorsal profile of head and body, from tip of snout to dorsal-fin origin, smoothly convex; straight posterior to dorsal-fin origin, smoothly tapering to caudal fin base. Head moderately depressed; lateral process of lateral ethmoid bone not visible dorsally. Snout rounded in dorsal view; smoothly concave anterior to naris. Posterior surface of bony pit of nasal organ sharply inclined. Trunk cross section between pectoral- and pelvic-fin origins horizontally ovoid, posterior to dorsal fin slightly rectangular, at level of two posteriormost trunk lateral plates slightly compressed.

Eyes moderately large, positioned slightly closer to posterior tip of compound pterotic than to tip of snout. Ventral margin of orbit located close to ventral surface of head. Dorsal interorbital distance shorter than ventral interorbital distance.

Total plates in lateral medial series 22–23 (23). Dorsal series plates 19–20 (19); middorsal series plates 3; midventral series plates 13–14 (13), with four plates anterior to first plate of ventral series; ventral series 19. Second plate of midventral series contacting a single plate of medial lateral series.

Abdomen covered by paired series of lateral sickle-shaped plates, with unequal number of plates between left and right sides, 4–8; medial series of 4–5 (5) roughly squared plates; anterior azygous plate absent; medial series occasionally absent, in which case paired series make contact along midline in fully developed individuals; abdominal shield fully developed in specimens greater ca. 30 mm SL. Single anal plate present. Thoracic plates absent. Canal in the preopercle present, semicircular; anteriormost pore located between ventral canal-bearing plate and fourth infraorbital; lateral margin of fourth infraorbital with notch for semicircular canal better defined than on posterolateral margin of canal-bearing plate.

Small odontodes evenly distributed on head. Odontodes on anterior rostral plate not arranged in well-defined series; no odontode-free discontinuity between ventral and dorsal odontode series; odontodes dorsal to tip of snout slightly larger than those on head. Odontodes on lamina of trunk plates arranged in longitudinal rows; progressive smoothing of plates with increased specimen size not observed; marginal odontodes on posterior border of trunk plates in specimens greater than 34 mm SL.

Total vertebrae 27. Premaxillary teeth 15–21 (18), dentary teeth 13–18 (15). Maxillary barbels short, not reaching ventral canal-bearing plate in adults.

Dorsal-fin origin located slightly posterior of vertical through pelvic-fin origin. Depressed dorsal fin reaching to vertical through posterior third of anal-fin length. Pectoral fin reaching to vertical through midpoint of pelvic-fin length. Pectoral fin reaching second half of pelvic-fin spine. Pectoral spine serrae extended along posterior margin of spine shaft, except for short basal segment; serrae oriented oblique to spine shaft. Pelvic fin short, longest branched rays slightly longer than spine; when depressed reaching to plate anterior to anal-fin spine. Caudal-fin posterior margin forked, upper and lower lobes not elongate. Adipose fin absent.

Color in alcohol

Ground color tan and pale ochre. Light to dark brown melanophores, clustered on trunk resulting in mottled appearance. Melanophores more densely concentrated on compound pterotic, supraoccipital, frontals, lateral rostral plates, at base of pectoral and anal fins, on anterior surface of lip, lateral half of branchiostegal membrane, and mesial portion of naris soft-tissue flap. Melanophores along dorsal midline between dorsal-fin base and caudal fin concentrated in irregular clusters, often defining darker outline on posterior margin of plates of dorsal series. Midlateral stripe situated along medial, midventral, and ventral series of plates, becomming progressively more pigmented between medial and ventral series. Ventral surface of body mostly unpigmented except for scattered melanophores on posterior portion of trunk, anterolateral to cleithral processes, on ventral canal-bearing plates and lateral portions of lateral abdominal plate series. Paired and unpaired fins with relatively numerous narrow, dark brown bars. Caudal-fin with 7–10 bands of brown melanophores on unbranched and branched rays. Series of lanceolate plates at caudal-fin base slightly darkened with black melanophores. Variably shaped dark brown to black spot over lower lobe of caudal-fin. Posteriormost plates of both dorsal and ventral series of lateral plates less pigmented, whitish.

Sexual dimorphism

Male urogenital papilla covered by flaplike anus. Males with patch of more tightly arranged small odontodes from fourth to sixth plates of ventral series, lateral to urogenital papilla. Female anus tubular, without separate urogenital papilla. In females, size and arrangement of odontodes on plates lateral to anus similar to those on adjacent plates, without distinct patch of differentially arranged odontodes.

Etymology

The specific epithet muzuspi is given in recognition of the Museu de Zoologia, Universidade de São Paulo, Brazil (MZUSP), as one of the leading institutional collections for ichthyology in South America. The name is treated as a noun in apposition to the generic name.

Distribution

Rio Tocantins basin; known only from Rio Agua Fria, in the drainage of Rio Araguaia (main tributary of Rio Tocantins) (fig. 27).

Fig. 29

Hypoptopoma spectabile, ANSP 136597, 23.4 mm SL male, in dorsal, lateral and ventral views.

TABLE 8

Morphometric and Meristic Data of Hypoptopoma spectabile Holotype: CAS 33806.

Holotype

CAS 33806, 22.5 mm SL, female, Quebrada Cramalote, Villavicencio, Dpto. Meta, Colombia; collected by M. González, 1914.

Paratypes (collected with holotype)

CAS 33807, 6 females and 2 males, 21.3–27.4 mm SL.

Non-Types

ANSP 136597 no data (5 ♀, 6 ♂, 20.9–24.5 mm SL). Colombia, Meta: ANSP 134008 (4 unsexed, 21.4–23.1 mm SL) Quebrada Venturosa between La Balsa and Puerto López; ANSP 134009 (1 ♀ + 1 ♂, 23.6–24.6 mm SL) Río Negro, downstream of Villavicencio–Puerto López hwy.; ANSP 134010 (2 ♀, 21.9–23.1 mm SL) same data than ANSP 134008; ANSP 134011 (♀, 21.9 mm SL) same data than ANSP 134009; ANSP 133767 (7 unsexed, 1 cs, 21.0–24.6 mm SL) caño Emma, El Viento ranch, 33.5 km NE Puerto López. Ecuador, Napo-Pastaza: FMNH 101545 (♂, 25.9 mm SL) Río Napo, 10.7 km upstream from bridge at Coca. Peru, Amazonas: LACM 41725-16 (3 unsexed, 24.9–25.9 mm SL) Río Santiago at La Poza; LACM 41726-18 (1 ♀ + 1 ♂, 24.3–26.6 mm SL) Río Santiago at La Poza; LACM 41729-36 (9 unsexed, 1 cs, 24.6–29.2 mm SL) Río Santiago at La Poza; LACM 41730-10 (1 ♂ + 1 ♀, 26.3–27.4 mm SL) Río Santiago at La Poza. Venezuela, Barinas: MCNG 6594 (7 unsexed, 21.9–23.9 mm SL) caño on the road between Puerta de Piedra and Santa Barbara. Bolivar: ANSP 139524 (1 unsexed, 18.4 mm SL) Quebrada Cuchivero, tributary of Río Matos. Portuguesa: CAS 64397 (2 unsexed, 19.2–19.8 mm SL) caño Maraca, km 60, Guanare to Guanarito Road.

Diagnosis

Hypoptopoma spectabile is distinguished from all congeners, except H. sternoptychum, by the pattern of abdominal plates, consisting of a pair of slender plates posterior to the coracoids followed by a series of 1–3 unpaired medial abdominal plates (Schaefer, 1996a: fig. 1a) (vs. two or three series of abdominal plates), by having the posterior process of the coracoids strongly curved, with its distal tip pointing dorsally (vs. posterior process smoothly curved, with its distal tip pointing posterodorsally), and by the absence of basipterygium fenestrae (vs. presence of basipterygium fenestrae). Hypoptopoma spectabile can be distinguished from H. sternoptychum by the absence of thoracic plates, fewer total lateral plates (20–22 (20) vs. 21–22 (21)), fewer dentary teeth (20–31 (24) vs. 21–37 (30)), narrow dorsal interorbital distance (mean dorsal interorbital distance 58.5 vs. 63.5), pelvic fin placed more anteriorly (mean abdominal length 12.7 vs. 15.5), shorter pectoral fin; length not reaching anal-fin origin, (mean pectoral-fin spine length 29.8 vs. 39.3), and by the absence of marginal odontodes (vs. marginal odontodes present in adults longer of 35 mm SL).

Description

Morphometric and meristic data presented in table 8. Body moderately robust; greatest body depth at dorsal-fin origin. Dorsal profile of head and body straight from tip of snout to supraoccipital, supraoccipital convex, nearly straight to dorsal-fin origin; slightly concave at dorsal-fin base; straight from posteriormost dorsal-fin ray to anteriormost procurrent caudal-fin ray. Ventral profile of head and body straight to slightly concave from tip of snout to anteriormost procurrent caudal-fin. Head depressed, almost as wide as cleithral width; lateral process of lateral ethmoid bone visible dorsally. Snout anterior margin parabolic in dorsal view; almost flat anterior to naris. Posterior surface of bony pit of nasal organ sharply inclined. Ventral surface flat from snout to anus, ovoid in cross section at anal base; caudal peduncle round in cross section.

Eyes moderate in size, positioned closer to posterior tip of compound pterotic than to tip of snout. Ventral margin of orbit located on lateral side of head. Dorsal interorbital distance shorter than ventral interorbital distance.

Total plates in medial series typically 20–22 (20). Dorsal series plates 18; middorsal series plates 4; midventral series plates 11–12, 3 plates anterior to first ventral series plate; ventral series plates 18. Second plate of midventral series contacting two plates of medial series.

Abdomen covered by one pair of slender plates posterior to coracoids, interdigitated at or near midline, followed by 1–2 medial unpaired rectangular to trapezoid-shaped plates. Single anal plate. Thoracic plates absent. Canal in preopercle present, semicircular; anteriormost pore located between ventral canal-bearing plate and fourth infraorbital, framed by notch at posterolateral margin of canal-bearing plate; notch on lateral margin of fourth infraorbital reduced.

Small odontodes evenly distributed on head; odontodes on anterior snout margin not arranged in well-defined series. No odontode-free discontinuity between ventral and dorsal odontode series; odontodes dorsal, ventral, and lateral to snout tip slightly larger than those on dorsal surface of head. Lamina of trunk plates with longitudinal rows of odontodes; marginal odontodes absent. Anterior margin of pectoral-fin spine and ventral surface of pelvic-fin spine with enlarged odontodes.

Total vertebrae 25. Premaxillary teeth 23–36 (29); dentary teeth 20–37 (30). Maxillary barbels short, reaching to anterior margin of ventral canal-bearing plate.

Dorsal-fin origin at vertical through middle of pelvic fin. Depressed dorsal fin surpassing vertical through end of anal-fin base. Depressed pectoral fin reaching to anus, not reaching to origin of anal fin. Pectoral spine serrae absent. Depressed pelvic fin reaching to anus. Caudal-fin margin moderately forked; upper and lower lobes equal. Adipose fin absent.

Color in alcohol

Ground color tan and pale ochre. Dorsal surface of head with clumped distribution of melanophores yielding mottled appearance, pigment concentrated in paired depression between tip of snout and nares. Sides of head and trunk with patchy distribution of melanophores, not arranged in distinct spots or bands; pigment slightly more concentrated between compound pterotic and dorsal cleithrum margin. Pigment arranged in series of three saddles between dorsal-fin origin and caudal fin; first saddle most intense and located at dorsal-fin origin, extending between nuchal plate and base of third branched dorsal-fin ray, and onto anterior dorsal-fin base; second saddle faint, comprised of scattered melanophores and located between base of last branched ray and posterior limit of dorsal fin when depressed; third saddle located midway between dorsal and caudal fins. Ventral surface of body mostly unpigmented, except for scattered melanophores on posterior portion of trunk and on anterior surface of lip. Paired and unpaired fins with few light dark brown bands. Dorsal fin with three light bands. Caudal fin with intense concentration of pigment at fin base; pigment extending slightly more posterior along length of ventralmost 3–4 caudal-fin branched rays, lanceolate plates at base of caudal fin light brown, continuous with basal pigmentation on caudal fin.

Sexual dimorphism

Male urogenital papilla elongated. Patch of tightly arranged small odontodes on four paired plates between pelvic-fin origin and anus. Males with soft-tissue flap on dorsal proximal surface of first branched pelvic-fin ray. Female anus tubular, without separate urogenital papilla. In females, size and arrangement of odontodes on plates lateral to anus similar to adjacent plates, without distinct patch of differentially arranged odontodes.

Distribution

Known from upland tributaries of the Río Amazonas in Colombia, Ecuador and Peru and tributaries of the upper Río Orinoco in Venezuela (fig. 27).

Fig. 30

Hypoptopoma sternoptychum, SU 36221, 30.6 mm SL female, in dorsal, lateral and ventral views.

TABLE 9

Morphometric and Meristic Data of Hypoptopoma sternoptychum Holotype: MUSM 4097.

Holotype

MUSM 4097, 33.2 mm SL, male (type locality: Quebrada Mariposa at Cusco-Amazonico Lodge, Puerto Maldonado, Tambopata, Dpto. Madre de Dios, Peru); collected by H. Ortega, 18 December 1989.

Paratypes

Bolivia, Beni: USNM 305836 (unsexed, 27.4 mm SL) E.B.B. Campamento Trapiche Pozo, on hour by dirt road from la Pascana; USNM 305600 (4 unsexed, 25.1–32.3 mm SL) Río Matos below road crossing, 48 km E of San Borja; USNM 305610 (5 unsexed, 1 cs, 29.2–36.5 mm SL) Río Curiraba, 10 km NE of El Porvenir Biol. Station, 40 air km E of San Borja. Brazil, Amazonas: USNM 177720 (female, 23.1 mm SL) Rio Urubu. Colombia, Amazonas: USNM 216851 (female, 33.4 mm SL) Leticia. Ecuador, Napo-Pastaza: FMNH 101542 (male, 36.6 mm SL) Río Aguarico, 1 river km above to mouth of the Río Lagartacocha, beach on both banks; FMNH 101546 (female, 32.5 mm SL) Río Napo, mouth of the Río Tiputini near Tiputini military barracks. Peru, Madre de Dios: MUSM 7551 (male, 32.1 mm SL) (collected with holotype); Loreto, SU 36221 (2 females, 23.7–30.6 mm SL).

Diagnosis

Hypoptopoma sternoptychum is distinguished from all congeners, except H. spectabile, by the pattern of abdominal plates, consisting of a pair of slender plates posterior to the coracoids followed by a series of 1–3 unpaired medial abdominal plates (Shaefer 1996a: fig. 1a) (vs. two or three series of abdominal plates), by having the posterior process of the coracoid strongly curved, with its distal tip pointing dorsally (vs. posterior process smoothly curved, with its distal tip pointing posterodorsally), and by the absence of basipterygium fenestrae (vs. presence of basipterygium fenestrae). Hypoptopoma sternoptychum can be distinguished from H. spectabile by the presence of thoracic plates, greater number of total lateral plates (21–22 (21) vs. 20–22 (20)), greater number of dentary teeth (21–37 (30) vs. 20–31 (24)), greater dorsal interorbital distance (mean dorsal interorbital distance 63.5 vs. 58.5), pelvic fin placed more posteriorly (mean pectoral-pelvic distance 15.5 vs. 12.7), and longer pectoral fin, length reaching or surpassing the anal-fin origin (mean pectoral-fin spine length 39.3 vs. 29.8).

Description

Morphometric and meristic data presented in table 9. Body moderately robust; greatest body depth at dorsal-fin origin. Dorsal profile of head and body straight from tip of snout to supraoccipital, supraoccipital convex, small tuft of 3–5 enlarged odontodes at posterior supraoccipital tip; trunk profile nearly straight to dorsal-fin origin; slightly concave at dorsal-fin base; straight from posteriormost dorsal-fin ray to anteriormost procurrent caudal-fin ray. Ventral profile of head and body straight to slightly concave from tip of snout to anteriormost procurrent caudal-fin ray. Head depressed, almost as wide as cleithral width; lateral process of lateral ethmoid bone visible dorsally. Snout anterior margin parabolic in dorsal view, lateral margins nearly straight, snout tip rounded; rostrum depressed anterior to nares. Posterior surface of bony pit of nasal organ sharply inclined. Ventral surface flat from snout to anus, ovoid in cross section at anal base; caudal peduncle round in cross section.

Eyes moderate in size, positioned closer to posterior tip of compound pterotic than to tip of snout. Ventral margin of orbit located on lateral side of head; eyes visible from below. Dorsal interorbital distance shorter than ventral interorbital distance.

Total plates in medial series typically 21–22 (21). Dorsal series plates 19; middorsal series plates 4; midventral series plates 12, three plates anterior to first ventral series plate; ventral series plates 19. Second plate of midventral series contacting two plates of medial series.

Abdomen covered by one pair of slender plates posterior to coracoids, interdigitated at or near midline, followed by 2–3 unpaired medial rectangular to trapezoid-shaped plates. Single anal plate. Thoracic plates present, 1–2 pairs. Canal in preopercle present, semicircular; anteriormost pore located between ventral canal-bearing plate and fourth infraorbital, framed by notch on posterolateral margin of canal-bearing plate; notch on lateral margin of fourth infraorbital reduced.

Small odontodes evenly distributed on head. Odontodes on anterior snout margin not arranged in well-defined series, no odontode-free discontinuity between ventral and dorsal odontode series; odontodes dorsal, ventral and lateral to snout tip slightly larger than those on dorsal surface of head. Lamina of trunk plates with longitudinal rows of odontodes; marginal odontodes present in mature adults. Anterior margin of pectoral-fin spine and ventral surface of pelvic-fin spine with enlarged odontodes.

Total vertebrae 26. Premaxillary teeth 23–36 (29); dentary teeth 21–37 (30). Maxillary barbels short, reaching to anterior margin of ventral canal-bearing plate.

Dorsal-fin origin at vertical through middle of pelvic fin. Depressed dorsal fin surpassing vertical through end of anal-fin base. Depressed pectoral fin surpassing origin of anal fin. Pectoral spine serrae absent. Depressed pelvic fin reaching to anus. Caudal-fin margin moderately forked; upper and lower lobes equal. Adipose fin absent.

Color in alcohol

Ground color tan and pale ochre. Dorsal surface of head with clumped distribution of melanophores, yielding mottled appearance. Pigmentation especially pronounced posterior to dorsal fin; pigment concentrated in paired depression between tip of snout and nares. Sides of head and trunk with patchy distribution of melanophores, arranged in distinct irregular blotches; pigment slightly more concentrated between compound pterotic and cleithrum dorsal margin. Pigment arranged in series of three saddles between dorsal-fin origin and caudal fin; first saddle most intense and located at dorsal-fin origin, extending between nuchal plate and base of third branched dorsal-fin ray, and onto anterior dorsal-fin base; second saddle faint, comprised of scattered melanophores and located between base of last branched rays and margin of fouth postdorsal plate; third saddle located midway between dorsal and caudal fins, occasionally separated from a fourth saddle by unpigmented area equal to one plate width. Ventral surface of body mostly unpigmented except for scattered melanophores on posterior portion of trunk and on anterior surface of lip. Paired and unpaired fins with few dark brown bands. Dorsal fin with three bands. Caudal fin with intense amorphous concentration of pigment at base. Lanceolate plates at base of caudal fin light brown.

Sexual dimorphism

Male urogenital papilla elongated. Patch of tightly arranged small odontodes on four paired plates between pelvic-fin origin and anus. Males with soft-tissue flap on dorsal proximal surface of first branched pelvic-fin ray. Female anus tubular, without separate urogenital papilla. In females, size and arrangement of odontodes on plates lateral to anus similar to adjacent plates, without distinct patch of differentially arranged odontodes.

Distribution

Known from tributaries from the upper Río Amazonas in Ecuador and Peru, and central Río Amazonas, including the upper Rio Madeira basin, in Bolivia and Peru (fig. 27).

Fig. 31

Hypoptopoma bianale, holotype, FMNH 105077, 53.7 mm SL female, in dorsal, lateral, and ventral views.

TABLE 10

Morphometric and Meristic Data of Hypoptopoma bianale Holotype: FMNH 105177. Paratypes: FMNH 117745; AMNH 243576. Nontypes: MNHG 2390.25; MZUSP 27624, 36203, 36206, 36207, 36208, 36211; SU 33272.

Holotype

FMNH 105077 (♀, 53.7 mm SL) Colombia: Amazonas, Amazon River at 2 to 3 miles upstream from Leticia; collected by Navarro et al., 13 November 1973.

Paratypes (all material collected with holotype)

FMNH 117745 (7 ♀ + 3 ♂, 2 cs, 37.2–47.9 mm SL); AMNH 243576 (1 ♀ + 1 ♂, 46.1–47.3 mm SL).

Non-Types

Peru, Loreto: MZUSP 36208 (1 ♀, 43.0 mm SL) Río Ucayali, Sgto. Lores; SIUC 28113 (1 ♀, 39.0 mm SL) Río Napo, confluence with Río Mazán, ca. 2–3 km N (town of) Mazán; SU 33272 (1 ♂, 42.6 mm SL) Río Ampiyacu. Ucayali: MHNG 2390.25 (1 ♀, 44.5 mm SL) Pucallpa, Río Ucayali, San Antonio; MZUSP 36206 (1 ♂, 43.2 mm SL) Pucallpa, Río Ucayali; MZUSP 36207 (1 ♀, 42.03 mm SL) Pucallpa, Río Ucayali, Laguna Yarinacocha. Brazil, Amazonas: MZUSP 27624 (1 ♀, 41.2 mm SL) Costa Japao, Baixao Rio Japurá, Mun. de Tefé; MZUSP 36211 (4 ♀, 41.0–51.8 mm SL) Rio Solimões, prox. I. Bururuá acima do boca do Jutaí.

Diagnosis

Hypoptopoma bianale is distinguished from all congeners by presence of two medial anal plates (vs. single medial anal plate in all other species of Hypoptopoma) (fig. 9C).

Description

Morphometric and meristic data presented in table 10. Body robust, stocky, greatest body depth at dorsal-fin origin, least depth at caudal peduncle. Dorsal profile of head and body straight from tip of snout to posterior tip of supraoccipital, smoothly convex at level of predorsal plates. Dorsal profile of trunk straight from dorsal-fin origin to caudal procurrent rays. Ventral profile of head and abdomen straight to slightly convex from snout tip to caudal-fin procurrent rays (not apparent in lateral view of head profile). Head moderately depressed, slightly acute, smoothly concave anterior to naris. Posterior surface of bony pit of nasal organ gradually inclined. Lateral process of lateral ethmoid bone slightly visible in dorsal view of head. Trunk cross section ovoid to progressively compressed posterior to dorsal fin.

Eyes moderately large, positioned slightly closer to posterior tip of compound pterotic than to tip of snout. Ventral margin of orbit close to ventral margin of head. Dorsal interorbital distance roughly equal to ventral interorbital distance.

Total plates in medial series 22. Dorsal series plates 19; middorsal series plates 3–4 (4); midventral series plates 12–13 (13), three plates anterior to first ventral series plate; ventral series plates 19. Second plate of midventral series contacting two plates of medial series.

Abdomen covered by paired series of lateral sickle-shaped plates, with unequal number of plates between left and right series, 4–6; anterior azygous plate present; lateral series make contact along midline in fully developed individuals. Presence of two medial anal plates positioned along longitudinal axis of body, between pelvic fins laterally, abdominal plates anteriorly, and anus posteriorly; anterior plate larger than posterior plate (fig. 9C). Thoracic plates present, 4–5. Canal in preopercle present, semicircular; anteriormost pore located between ventral canal-bearing plate and fourth infraorbital, framed by notch at posterolateral margin of canal-bearing plate and lateral margin of fourth infraorbital.

Small odontodes evenly distributed on head. Odontodes on rostral margin of snout enlarged and arranged in irregular lines, without odontode-free discontinuity between dorsal and ventral margins. Lamina of trunk plates with odontodes arranged in longitudinal rows; plates progressively smoother in ontogeny; marginal odontodes present in mature adults. Anterior margin of pectoral-fin spine and ventral surface of pelvic-fin spine with enlarged odontodes.

Total vertebrae 26. Premaxillary teeth 21–29 (25), dentary teeth 20–27 (23). Maxillary barbels extending slightly beyond anterior margin of ventral canal-bearing plate.

Dorsal-fin origin located at vertical through pelvic-fin origin; depressed dorsal fin reaching almost to vertical through posterior tip of anal fin. Pectoral fin reaching to vertical through posterior tip of pelvic fin. Pectoral spine serrae along entire posterior margin, except for short basal segment; individual serrae oriented oblique to spine shaft. Pelvic fin short, unbranched and first branched rays equal in length; when depressed reaching to plate anterior to anal-fin spine. Caudal-fin margin concave. Adipose fin absent.

Color in alcohol

Overall body pigmentation relatively uniform, ground color tan to pale ochre. Melanophores variably light brown, slightly more concentrated along base of plates, dorsal portions of head, lateral border of compound pterotic, cleithral process, opercle, and base of dorsal fin. No lateral stripe on trunk. Ventral surface of body mostly unpigmented. Scattered dark melanophores present on anterior surface of lip. Fins with pale brown bands (dorsal fin 4–6; caudal fin 4–5). Triangular spot of dark brown melanophores at base of caudal-fin branched rays, mostly extended over basal plates and lower lobe, progressively widening toward lower marginal ray; caudal-fin bars mainly visible on marginal rays and outer most branched rays.

Sexual dimorphism

Male urogenital papilla short, half-length of flaplike anus, which totally covers and joins base of papilla. Males with patch of tightly arranged small odontodes on second through fourth plates of ventral series, lateral to urogenital papilla. Female anus tubular, without separate urogenital papilla. In females, size and arrangement of odontodes on plates lateral to anus similar to adjacent plates, without distinct patch of differentially arranged odontodes.

Distribution

Rio Solimões in Brazil and Río Ucayali in Peru (fig. 32).

Fig. 32

Drainage map of South America showing distribution of H. bianale (dots + circle), H. inexspectatum (squares), H. steindachneri (triangles), and H. elongatum (stars). Open symbols designate type localities; some symbols represent more than one locality record.

Etymology

The specific epithet bianale is a reference to the presence of two anal plates (Lt. bi, meaning “two”; Lt. analis, from anal (adaptation from modern Latin; Oxford English Dictionary: “Of or pertaining to the anus, or excretory opening”).

Fig. 33

Hypoptopoma inexspectatum, holotype, MACN 5164, 53.6 mm SL, in dorsal, lateral, and ventral views.

TABLE 11

Morphometric and Meristic Data for Hypoptopoma inexspectatum Holotype: MACN 5164. Nontypes: ILPLA 268, 269, 270, 875 (morphometric data only); NRM 22832 (meristic data only).

Holotype

MACN 5164 (53.6 mm SL) Argentina: Río Paraguay, near Formosa city; collected by Solari, March 1885.

Other Material Examined

Argentina, Buenos Aires: ILPLA 875 (1 ♂, 51.7 mm SL) Río Paraná drainage, Río Yaguarón, San Nicolás, Balneario Rio Municipal; MACN 6547 (1) Buenos Aires, Palermo, Lago. Corrientes: ILPLA 268 (1 ♀, 44.7 mm SL) Isla Toro; ILPLA 269 (20 ♀ + 20 ♂, 16 cs, 34.0–68.4 mm SL) Río Paraná, Tuyutí; ILPLA 270 (2 ♂42.8–60.8) Río Paraná; MACN 7014 (5) Río Santa Lucía; MZUSP 10262 to MZUSP 10273 (12, 15.7–55.2 mm SL) Paso de la Patria, Río Paraná. Formosa: MACN 3244 (3) Río Formosa. Misiones: FMNH 71344 (1 ♂, 0.5 mm SL) Río Paraná. Santa Fe: MACN 7013 (3) Helvecia, Arroyo Cigueña; MACN 7015 (+100) Helvecia; MFA-Z-VI.798 (n  =  2, 35.5–36.9 mm SL) Dpto. Capital, Río Paraná drainage, riacho Santa Fe. Bolivia, Santa Cruz: FMNH 59593 (5 ♀ + 12 ♂, 46.6–62.9 mm SL) Puerto Suárez. Brazil, Mato Grosso: BMNH 1895.5.17.77-82 (paratypes of Hypoptopoma guentheri) (3 unsexed, 43.0–55.0 mm SL) Mato Grosso; FMNH 59617 (2 ♀ + 3 juveniles, 29.2–61.1 mm SL) Cáceres, Rio Paraguay; FMNH 59618 (2 juveniles, 35.0–39.7 mm SL) Campo Alegre, Rio Jaurú; FMNH 59619 (1 juvenile, 31.1 mm SL) Campo Alegre, Rio Jaurú; FMNH 69999 (1 ♀ + 1 ♂ + 1 juvenile, 40.1–61.7 mm SL) Descalvados, Rio Paraguay; FMNH 71329 (8 ♀ + 4 ♂ + 1 juvenile, 40.6–67.8 mm SL) Conceição, Rio Paraguay; FMNH 71330 (2 juveniles, 30.9–37.9 mm SL) Campo Alegre, Rio Jaurú, into Rio Paraguay; FMNH 71331 (7 ♀ + 2♂, 50.7–58.0 mm SL) Descalvados, Rio Paraguay; MNRJ 5829 (1) Jacaré, Rio Kolueme; MZUSP 44391 (26 unsexed, 30.6–52.8 mm SL) Rio Paraguay at Cáceres and surroundings; USNM 326344 (26 ♀, 37.9–60.9 mm SL) Rio Paraguay at Cáceres and surroundings. Mato Grosso do Sul: FMNH 108587 (4 ♀ + 8 ♂ + 2 juveniles) Rio Negro at road between Nhecolandia and BR 262; MNRJ 1083 (2 unsexed) Porto Esperança; MZUSP 28339 (3 ♀, 35.0–39.0 mm SL) Rio Pixaim, Transpantaneira highway; MZUSP 36183 (1 ♀, 35.8 mm SL) Rio Pequiri, mun. of Coxim; MZUSP 36210 (1 ♀, 35.8 mm SL) tributary of Rio Cuiba, mun. of Cuiba; MZUSP 36223 (62 ♀ + 1 ♂, 34.2–57.5 mm SL) Boca do Croara, Río Cuiba, mun. of B. de Melgaco; MZUSP 36344 (2 unsexed, 36.7–43.6 mm SL) Ladario, Codrasa, Corumba; MZUSP 38034 (1, 49.7 mm SL) Rio Paraguay, Morrinhos, mun. Corumbá. Paraguay, Alto Paraguay: FMNH 108109 (3 ♀ + 3 juveniles, 26.2–65.8 mm SL) Rio Paraguay, Estancia Voluntad at Puerto Voluntad; FMNH 108110 (2 ♀ + 7 juveniles, 28.1–50.3 mm SL) Riacho Vaqueiro, ca. 2 km above Fuerte Olympo, at base of Cerro Barrero; FMNH 108111 (1 ♀, 50.2 mm SL) Río Paraguay at left margin, above Estancia Cerrito; NRM 22832 (57 ♀, 31.3–59.5 mm SL) Río Paraguay at Estancia Doña Julia and halfway between estancia and village of Bahía Negra. Amambay: MHNG 2160.32 (3 ♂, 51.3–57.6 mm SL) arroyo Apa-mi (10 km Sud-Este de Bella Vista). Central: MHNG 2475.63 (4 ♀ + 2 ♂, 50.1–61.5 mm SL) San Antonio, Río Paraguay; MHNG 2515.9 (2 ♀ + 4 ♂, 61.4–67.9 mm SL) San Antonio, Río Paraguay; UMMZ 205878 (1 ♂ + 10 juveniles, 3 cs, 11.5–51.8 mm SL) E shore Río Paraguay, 1.0 km S of Puente Remanso bridge. Concepción: FMNH 108112 (1 juvenile, 37.2 mm SL) Río Apa, left margin, above San Carlos; MHNG 2353.24 (1 ♂, 54.8 mm SL) Laguna Negra, 15 km. Est. de Paso Bareto; MHNG 2531.70 (2 ♂, 58.5–63.1 mm SL) Riacho La Paz, a 6 km, North to Estancia Primavera. Presidente Hayes: FMNH 59621 (4 ♀, 47.3–59.9 mm SL) Villa Hayes; FMNH 77083 (1 ♀, 70.8 mm SL) Villa Hayes; MHNG 2231.65 (2 ♀, 45.3 mm SL) Río Negro, a 160 km route du Transchaco. San Pedro: MHNG 2353.26 (2 ♀, 63.5–68.2 mm SL) Río Jejuí Guazú at Jejuí.

Diagnosis

Hypoptopoma inexspectatum is distinguished from all congeners by having the odontodes on the snout margin, the rostral plate, and first and second infraorbitals arranged in regular series. Along the rostral margin, the dorsal and ventral series are separated by an odontode-free discontinuity approximately as wide as the base of individual odontodes. Along the first and second infraorbitals, the discontinuity becomes narrower, but forms a dividing line between ventral and dorsal odontode series (fig. 16). The odontode arrangement becomes more irregular posterolateral to the second infraorbital, and individual odontodes become roughly oriented with the trunk axis. In contrast, in all other species of Hypoptopoma, the ventral and dorsal odontodes on the rostrum are variably separated and/or covered by soft tissue, and odontodes are typically not clearly aligned in series.

Description

Morphometric and meristic data presented in table 11. Body moderately elongate; greatest body depth at dorsal-fin origin. Dorsal profile of head and body straight to slightly convex from tip of snout to posterior tip of supraoccipital; straight from dorsal-fin origin to anteriormost procurrent caudal-fin ray; straight from tip of snout to anteriormost procurrent caudal-fin ray. Head moderately depressed, slightly narrower than cleithral width; lateral process of lateral ethmoid visible dorsally, short. Snout slightly spatulate in dorsal view (fig. 34A); slightly concave dorsally anterior to naris. Posterior surface of bony pit of nasal organ sharply inclined. Trunk cross section between pectoral- and pelvic-fin origins slightly triangular, ovoid to progressively compressed posterior to dorsal fin.

Fig. 34

Hypoptopoma inexspectatum, ILPLA 875, 51.7 mm SL male, in dorsal, lateral, and ventral views.

Eyes relatively large, positioned slightly closer to posterior tip of compound pterotic than to tip of snout. Ventral margin of orbit located on ventral surface of head. Dorsal interorbital distance/ventral interorbital distance ratio changing from <1 to >1 during ontogeny.

Total plates in lateral medial series 20–22 (21). Dorsal series plates 17–18 (18); middorsal series plates 3; midventral series plates 11–12 (12), three plates anterior to first plate of ventral series; ventral series plates usually 17–18 (18). Second plate of midventral series contacting two plates of medial series.

Abdomen covered by paired series of lateral sickle-shaped plates, with unequal number of plates between left and right series, 4–7 each; anterior azygous plate present; medial plates, if present, not forming well-defined series (in 3 of 101 individuals examined). Single anal plate present. Thoracic plates present, 2–6. Canal in preopercle present, semicircular; anteriormost pore located between ventral canal-bearing plate and fourth infraorbital, framed by notch at posterolateral margin of canal-bearing plate and lateral margin of fourth infraorbital.

Small odontodes evenly distributed on head. Odontodes on rostral margin of snout, rostral plate, first and second infraorbitals arranged in regular series. Along rostral plate, dorsal and ventral series separated by odontode-free discontinuity approximately as wide as base of individual odontodes; along first and second infraorbitals, discontinuity becoming narrower but still clearly separating ventral and dorsal series. Lamina of trunk plates with longitudinal rows of odontodes and becoming progressively smoother ontogenetically; marginal odontodes present in mature adults.

Total vertebrae 25. Premaxillary teeth 15–20 (18); dentary teeth 17–17 (15). Maxillary barbels short, reaching slightly beyond anterior margin of ventral canal-bearing plate in adults.

Dorsal-fin origin located slightly posterior to vertical through pelvic-fin origin. Depressed dorsal fin reaching to vertical through posterior half of anal-fin base. Depressed pectoral fin reaching anus, not reaching to insertion of anal-fin spine. Extension of serrae along pectoral spine margin reduced ontogenetically from proximal two-thirds in smaller specimens to middle third in larger specimens; individual serrae oriented orthogonal to spine shaft. Pelvic fin short, unbranched and first branched rays of equal length. Depressed fin reaching to anus, but not reaching to insertion of anal-fin spine. Caudal-fin margin broadly concave; upper and lower lobes equal. Adipose fin variably present.

Color in alcohol

Ground color tan brown, lighter on ventral region of head and trunk. Darker longitudinal stripes anterior to naris. Dark to diffuse midlateral stripe along plates of medial series. Darker bands posterior to dorsal-fin base variably defined. All fins with brown bars, more pronounced along unbranched rays. Tips of branched rays distally hyaline. Basal darker spot at base of caudal-fin lower lobe.

Sexual dimorphism

Male urogenital papilla present. Males with patch of tightly arranged small odontodes oriented as a swirl covering second, third, and fourth plates of ventral series, lateral to urogenital papilla. Female anus tubular, without separate urogenital papilla. In females, size and arrangement of odontodes on plates lateral to anus similar to adjacent plates, without distinct patch of differentially arranged odontodes.

Distribution

Río Paraguay and Río Paraná drainage basin. There are no records for the upper Paraná upstream of Salto das Sete Quedas (Mato Grosso do Sul, Brazil) (fig. 32).

Taxonomic Remarks

Holmberg (1893a) erected the genus Aristommata for his new species A. inexspectata, based on a single specimen from the Río Paraguay. While the synonymy of Aristommata and Hypoptopoma was subsequently recognized by Berg (1898), the taxonomic status of H. inexspectata remained unsettled. Although considered a valid species in several checklists and faunal studies, the specific name was also regarded at various times as a junior synonym of H. joberti (Berg, 1898), of H. guentheri (Fowler, 1915), or of H. gulare (Gosline, 1945). The first extensive monograph on loricariids (Regan, 1904) ignored H. inexspectata, and more recently, Boeseman (1974) included it among the “obscure species” of the loricariid subfamily Hypoptopomatinae. The examination of type specimens and additional comparative material provided new character evidence to support the taxonomic status of H. inexspectata (Aquino, 1997; Aquino and Miquelarena, 2000).

Boulenger (1895) described the species Hypoptopoma guentheri based on “numerous specimens” from Descalvados (Mato Grosso, Brazil). Berg (1898) listed H. guentheri as a junior synonym of H. inexspectata, an opinion shared by Eigenmann (1910), Ringuelet et al. (1967), and Aquino (1997). Our examination of the syntype series and extensive collections of Hypoptopoma specimens from the Paraguay-Paraná system serve to confirm that action.

Fig. 35

Hypoptopoma elongatum, holotype, INPA 7240, 95.4 mm SL, female, in dorsal, lateral, and ventral views.

TABLE 12

Morphometric and Meristic Data for Hypoptopoma elongatum Holotype: INPA 7240. Paratype: INPA 29657. Nontype: MZUSP 38187.

Holotype

INPA 7240 (♀, 95.4 mm SL) Brazil: Pará, Rio Tapajos, Itaituba; collected by L. Rapp Py-Daniel and J. Zuanon, 18 October 1991.

Paratypes

INPA 29657 (32 ♀ + 26 ♂, 2 cs, 62.7–102.7 mm SL) (collected with holotype).

Other Material Examined

Brazil, Pará: CAS 6748 (1 ♀, 93.2 mm SL) Santarem market; INPA 5405 (6 ♀, 93.0–96.2 mm SL) Rio Trombetas, Cach. Porteira a jusante da cachoeira; INPA 5406 (1 ♀, 101.4 mm SL) Rio Trombetas, Lago Tapagem; INPA 5570 (3 ♀, 88.4–104.2 mm SL) Rio Trombetas, R. Cumina, Lago Salgado; INPA 7130 (1 ♀ + 2 ♂, 90.6–94.1 mm SL) Rio Cupari, afluente do Rio Tapajos (próximo a boca); INPA 7131 (3 ♀ + 1 ♂, 88.8–94.3 mm SL) Rio Cupari, afluente do Rio Tapajos (próximo a boca); INPA 7213 (2 ♀, 88.2–9.2 mm SL) Rio Cupari, afluente do Rio Tapajos; MZUSP 34193 (8 ♀ + 3 ♂, 87.9–97.0 mm SL) Rio Tapajos, beira do rio, entre Itaituba e São Luis; MZUSP 36187 (2 ♀ + 2 ♂, 79.9–89.5 mm SL) Rio Tapajos, ihla confrontando Monte Cristo; MZUSP 36220 (1 ♀, 77.0 mm SL) Rio Tapajos, Igarape Jacare, margen dereita do Rio Tapajos, perto de Boim.

Diagnosis

Hypoptopoma elongatum is distinguished from all congeners by having a nonpigmented band on the head positioned parallel to the ventral margin of the rostral and lateral snout plates, with the margin between pigmented and nonpigmented plates very well defined (fig. 35C) (vs. absence of a distinct pigmented band). Hypoptopoma elongatum can be further distinguished from congeners, except for H. inexspectatum, by having the ventral surface of the anterior rostral plate as wide as the ventral surface of the first lateral rostral plates (vs. ventral surface gradually widening from anterior rostral to lateral rostral plates). Hypoptopoma elongatum is readily distinguished from H. inexspectatum by having a greater number of plates along the trunk medial series (23 vs. 20–21 (21)), by having the snout appearing pointed in dorsal view due to a slight concavity between rostral plate and first infraorbital (fig. 35A) (vs. snout typically spatulate), and by having, if present, a distinct series of odontodes along dorsal and ventral rostral margin of snout restricted to the anterior rostral plate (vs. series of odontodes along dorsal and ventral rostral margin of snout extended laterally to include second and third infraorbitals).

Description

Morphometric and meristic data presented in table 12. Body robust; greatest body depth at dorsal-fin origin. Dorsal profile of head and body straight from snout tip to dorsal-fin origin, slightly elevated at posterior tip of supraoccipital; straight from dorsal-fin origin to anteriormost procurrent caudal-fin ray. Ventral profile of head and body straight to slightly concave from snout tip to anteriormost procurrent caudal-fin ray. Head moderately depressed, almost as wide as cleithral width; lateral process of lateral ethmoid bone visible dorsally. Anterior snout margin acute; slightly concave anterior to naris. Posterior surface of bony pit of nasal organ sharply inclined. Trunk cross section slightly triangular between pectoral- and pelvic-fin origins, ovoid to progressively round posterior to dorsal fin, caudal peduncle posterior to adipose-fin base progressively compressed.

Eyes relatively large, positioned closer to posterior tip of compound pterotic than to tip of snout. Ventral margin of orbit located on ventral side of head. Dorsal interorbital distance greater than ventral interorbital distance.

Total plates in medial series typically 23. Dorsal series plates 20; middorsal series plates 4; midventral series plates 12–13 (13), three plates anterior to first ventral series plate; ventral series plates 20. Second plate of midventral series contacting two plates of medial series.

Abdomen covered by paired series of lateral sickle-shaped plates, with unequal number of plates between left and right series, 4–7 each; anterior azygous plate usually present. Single anal plate. Thoracic plates present, 2–6. Preopercular canal in preopercle present, semicircular; anteriormost pore located between ventral canal-bearing plate and fourth infraorbital; framed by notch at posterolateral margin of canal-bearing plate and ventral margin of fourth infraorbital.

Small odontodes evenly distributed on head; odontodes on rostral margin not arranged in well-defined series, without odontode-free discontinuity. Odontodes on ventral surface of rostral plate variably enlarged. Lamina of trunk plates with odontodes arranged in longitudinal rows, becoming progressively smoother ontogenetically; marginal odontodes present in mature adults. Anterior margin of pectoral-fin spine and ventral surface of pelvic-fin spine with enlarged odontodes.

Total vertebrae 27. Premaxillary teeth 16–23 (21); dentary teeth 14–22 (18). Maxillary barbels short, only reaching to anterior margin of ventral canal-bearing plate.

Dorsal-fin origin located slightly posterior to vertical through pelvic-fin origin. Depressed dorsal fin reaching to or surpassing vertical through posterior half of anal-fin base. Depressed pectoral fin reaching to anus. Pectoral spine serrae typically along middle three-fifths of spine length, involving less of spine shaft with growth; individual serrae oriented oblique to spine shaft. Pelvic fin short, unbranched and first branched rays of equal length. Depressed pelvic fin reaching to anus, not reaching anal-fin origin. Caudal-fin margin markedly forked; upper and lower lobes equal. Adipose fin variably present; when present, small and membranous.

Color in alcohol

Ground color tan and pale ochre. Light to dark brown melanophores clustered on trunk and at base of plates, yielding mottled appearance. Melanophores slightly more concentrated on narrow area along compound pterotic, between cleithral process and opercle, and at base of both dorsal and pectoral fins. Well-defined nonpigmented band parallel to ventral surface of snout plates, including two plates lateral to barbel; margin between pigmented and nonpigmented plates distinct. Deep-lying melanophores arranged in series of blotches posterior to dorsal-fin base; butterfly-shaped blotch anterior to dorsal-fin origin, centered at anteriormost predorsal plate, anterior arms lateral to supraoccipital. Trunk lateral stripe involving medial plate series. Ventral surface of body mostly unpigmented except for scattered melanophores on posterior portion of trunk and anterior surface of lip. Paired and unpaired fins with few dark brown bands. Dorsal fin typically with faint bar at base followed by one dark bar roughly orthogonal to rays and closer to tip than to base of fin, with one or two additional faint bars intervening. Caudal-fin rays with melanophores arranged in parallel V-shaped pigmented bands, typically fainter on medial branched rays; anterior band located at base of branched rays, typically lighter than posterior band; posterior band located near posteror fin margin; unbranched rays and tip of median caudal-fin branched rays light. Lanceolate plates at base of caudal fin light brown, variably connected with basal faint vertical band.

Sexual dimorphism

Male urogenital papilla well developed, pointed, joined at base to anterior flaplike anus. Patch of tightly arranged small odontodes on second, third, and fourth plates of ventral series, lateral to urogenital papilla. Males with soft-tissue flap along posterior margin of pelvic spine and along basal one-third to two-thirds of spine. Female anus tubular, without separate urogenital papilla. In females, size and arrangement of odontodes on plates lateral to anus similar to adjacent plates, without distinct patch of differentially arranged odontodes.

Distribution

Lower Rio Tapajos and lower Rio Trombetas (fig. 32).

Etymology

The specific epithet elongatum (Lt. elongatus, meaning “prolonged”) is a reference to the elongated general shape of the body, particularly marked at the tip of snout, caudal peduncle, and caudal fin.

Fig. 36

Hypoptopoma incognitum, holotype, AMNH 39759, 85.01 mm SL, female, in dorsal, lateral, and ventral views.

TABLE 13

Morphometric Data for Hypoptopoma incognitum Holotype: AMNH 39759. Paratype: AMNH 241976. Nontypes: CAS 6736, 6748, 56723; FMNH 117743; INPA 2798, 6039; MUSM 7520, 10521; MZUSP 4978; UMMZ 202339; USNM 177706, 177707, 308093.

Holotype

AMNH 39759, 85.01 mm SL, female, Bolivia: Beni, Río Itenez, opposite to Costa Marques; collected by R.M. Bailey and R. Ramos, 1–3 September 1964.

Paratypes (collected with holotype)

AMNH 241976, 6 females and 13 males, 2 cs, 76.6–94.1 mm SL. UMMZ 204339, 8 females and 8 males, 3 cs, 79.56–95.03 mm SL.

Other Material Examined

Bolivia, Beni: AMNH 40039 (1 ♂, 85.4 mm SL) Río Baures, above mouth 6 km SW Costa Marques, Brazil; AMNH 77403 (1 ♂, 72.1 mm SL) Río Mamoré, ca. 10 km west of San Pedro; AMNH 77467 (2 ♀ + 1 ♂, 43.5–57.3 mm SL) Río Mamoré, Puerto Siles; CAS 77140 (1 ♂, 56.7 mm SL) Cachuela Esperanza, first falls of the Beni; CBF 1323 (5 ♀, 53.1–78.9 mm SL) Ballivian, Espíritu, Arroyo Carnaval, Río Yacuma, Mamoré, Madeira; USNM 305596 (2 ♀, 47.2–49.2 mm SL) Río Matos/Apere/Mamoré; Prov. Ballivia, Río Matos below road x-ing, 48 km E San Borja. Pando: FMNH 107001 (2 ♀, 48.0–62.3 mm SL) 100 m de la boca del Nareuda en el Tahuamanu; FMNH 107002 (2 ♀, 36.4–39.1 mm SL) Río Nareuda, río arriba de la desembocadura en el Tahuamanu; FMNH 107003 (7 ♀, 41.8–71.1 mm SL) Río Manuripi, +/− 12 km río arriba de Puerto Rico; FMNH 107004 (2 ♀ + 2 ♂, 54.5–71.5 mm SL) Río Manuripi, +/− 20 km río arriba de Puerto Rico; FMNH 107007 (1 ♀, 71.3 mm SL) Brazo del Manuripi, +/− 1 km río arriba del campamento; FMNH 107008 (8 ♀, 50.2–70.6 mm SL) Río Manuripi above camp; FMNH 107009 (3 ♀ + 2 ♂, 52.8–82.1 mm SL) Río Manuripi at playa, 5.78 km from camp, 9.23 from Puerto Rico; FMNH 107010 (2 ♀ + 2 ♂, 65.1–73.6 mm SL) Río Manuripi at playa outside, 6.76 km above camp and 9.78 above Puerto Rico; FMNH 107011 (1 ♀, 34.6 mm SL) Rio Manuripi at island 0.76 km above camp and 4.20 above Puerto Rico. Santa Cruz: CBF 2862 (1 ♀, 53.9 mm SL) Guarayos, Perseverancia, Río Negro cerca de Las Naranjas; CBF 10110 (1 ♀, 51.1 mm SL) Guarayos, Perseverancia, Río Negro. Brazil, Acre: MZUSP 49782 (3 ♀ + 1 ♂, 45.5–46.9 mm SL) Rio Acre, entre Seringal Paraiso y Lago Amapa; MZUSP 49795 (1 ♀ + 1 ♂, 75.2–85.7 mm SL) Lago Amapa. Amazonas: CAS 56723 (1 ♀, 74.0 mm SL) Igarapé Chibareno, 30 km E of Manaus on south shore of Rio Negro, about 0.3 mi. S of its entrance into Rio Amazonas; INPA 127 (4, 51.3–70.4 mm SL) Lago Janauaca, Rio Solimões; INPA 807 (1 ♀, 84.0 mm SL) Flutuante do Tarumã Açu; INPA 2798 (9 ♀ + 4 ♂, 2 cs, 58.9–88.3 mm SL) Ihla da Marchantaria, Rio Solimões; INPA 2800 (1, 74.1 mm SL) Lago Janauaca, Rio Solimões; INPA 6035 (3 ♀, 82.0–85.6 mm SL) Rio Amazonas, Ihla do Careiro, Lago do Pedro; INPA 6082 (1 ♂, 78.8 mm SL) Rio Solimões, Boca do Paraná do Janauacá; INPA 6088 (1 juvenile, 58.8 mm SL) Río Madeira, Igarapé Aramaguara; INPA 14017 (1 ♂, 76.2 mm SL) Rio Solimões, Parana do Rei; MZUSP 6723 (1 ♀, 74.1 mm SL) Rio Negro, Manaus; MZUSP 7557 (1 ♀ + 1 ♂, 64.9–68.2 mm SL) Parana do Urucura, mun. de Urucura; MZUSP 7654 (1 ♀, 75.5 mm SL) Boca do lago José Açu, Parintins; MZUSP 6598 (1 ♀, 74.4 mm SL) Lago Manacupuru; MZUSP 27607 (1 ♀, 67.0 mm SL) Paraná de Capacete, Rio Solimões, mun. de Benjamin Constant; MZUSP 36198 (1 ♀, 90.0 mm SL) Lago Janauaca e arrededores, Rio Solimões; MZUSP 36227 (1 juvenile, 43.3 mm SL) Ihla Marchantaria, perto de Manaus; USNM 177706 (1 ♀, 62.3 mm SL) Amazonas, Rio Urubu; USNM 177707 (1 ♀, 65.95 mm SL) Amazonas, Rio Urubu; USNM 306963 (2 juveniles, 37.3–41.0 mm SL) ressaca da Ilha de Marchantaria; USNM 306991 (1 juvenile, 41.8 mm SL) ressaca da Ilha de Marchantaria; USNM 307056 (1 ♂, 62.24 mm SL) Amazonas, Paraná de Janauaca, entrada do Lago Castanho; USNM 308093 (1 ♂, 82.9 mm SL) Amazonas, entrada de Janauari, entre Furo de Paracuuba e Lago Terra Preta; USNM 308244 (1 ♂, 83.2 mm SL) near Manaus, entrance of lago Janauari, between furo (channel) de Paracuuba and lago Terra Preta; USNM 308303 (1 ♂, 79.0 mm SL) Amazonas, Lago Terra Preta, Janauari. Goiás: MZUSP 4881 (11, 39.2–71.0 mm SL) Rio Araguaia, Aruana. Maranhão: MNRJ 17720 (8) Rio Mearim em Arari; MNRJ 17725 (4) Rio Mearim; MNRJ 17726 (1) Lago Malhada Grande. Mato Grosso: MZUSP 36222 (1 juvenile, 47.6 mm SL) Río Araguaia, Santa Terezinha. Pará: CAS 6736 (1 ♀, 70.3 mm SL) Amazonas, Santarém market; CAS 6748 (1 ♀, 92.4 mm SL) Amazonas, Santarém market; FMNH 59622 (3 ♀, 47.0–55.6 mm SL) Santarém; FMNH 117743 (13 ♀ + 2 ♂, 41.6–72.3 mm) Santarém; INPA 558 (2) Rio Tocantins, Ig. Arapari, Breu Branco; INPA 6028 (1) Rio Tocantins, Breu Branco; INPA 6029 (1) Rio Tocantins, Poco do Paulo; INPA 6030 (1) Rio Tocantins, Breu Branco, Igarape Arapari; INPA 6031 (2) Rio Tocantins, Breu Branco, Igarape Canoal; INPA 6032 (1) Rio Tocantins, Breu Branco, Igarape Arapari; INPA 6033 (3) Rio Tocantins, Itupiranga; INPA 6036 (5) Rio Tocantins, a jusante da represa; INPA 6037 (1) Rio Tocantins, Breu Branco, Igarape Canoal; INPA 6039 (13) Rio Tocantins, Itupiranga; INPA 6053 (9) Rio Tocantins, Igarape Arapari, Breu Branco; INPA 6054 (1) Rio Tocantins, Icangui; INPA 6055 (2) Rio Tocantins, Capuerana; INPA 6057 (1) Rio Tocantins, Tucurui, Igarape Vallentim; INPA 6058 (1) Rio Tocantins, Itupiranga; INPA 6059 (1) Rio Tocantins, Breu Branco, Igarape Canoal; MHNG 2538 12 (1 ♀, 48.1 mm SL) Ig. Azul, Ilha do Cameta, face a Santarém; MHNG 2708.060 (1 ♂, 71.7 mm SL) Amazon river, side arm with lagos along right shore, about 10 km downriver of Santarém; MZUSP 5657 (6 juveniles, 19.1–39.8 mm SL) Lago Paru, Oriximiná; MZUSP 7850 (3 ♀, 63.5–69.7 mm SL) Parana Jacaré, Mun. Faro; MZUSP 8539 (1 ♀, 76.7 mm SL) Rio Tapajos, Santarém; MZUSP 34194 (1 ♀, 89.6 mm SL) Tocantins, Tucurui; MZUSP 36185 (1 ♀, 71.7 mm SL) Rio Arari, Cachoeira de Arari, Ilha de Marajo; MZUSP 36186 (2 ♀, 57.2–80.4 mm SL) Lagoa marginal do Rio Tocantins, perto de Baiao; MZUSP 36188 (1 ♀, 64.9 mm SL) Oriximiná. Rondonia: INPA 456 (16 ♀ + 9 ♂, 63.0–75.0 mm SL) Río Madeira, Varza de calama, Lago de Repartimento; INPA 2237 (1 ♀, 70.0 mm SL) Río Madeira, Calama Flechal. Roraima: INPA 49 (1 ♀, 86.1 mm SL) Paraná do Rio Branco. Peru, Madre de Dios: ANSP 144008 (1 ♀, 65.9 mm SL) NW of Puerto Maldonado, Lago Tupuhumaro, oxbow lake E bank of Madre de Dios, above junction with Río de las Piedras; MUSM 2474 (5 ♀, 40.6–66.6 mm SL) Manú, Parque Nacional, Pakitza, Cocha Salvador; MUSM 7520 (1 ♀ + 5 ♂, 33.2–65.8 mm SL) Tambopata, Río Madre de Dios, Lago Valencia; MUSM 7960 (1 ♀, 55.1 mm SL) Tambopata, Río Madre de Dios, Lago Valencia; MUSM 8123 (3 ♀, 60.2–65.2 mm SL) Tambopata, Candamo, Río Tambopata, Río Chuncho; USNM 263910 (3 ♀, 46.4–69.6 mm SL) Reserva Natural de Tambopata, Laguna Cocococha, 5.1 km to E of explorers inn; USNM 264046 (2 juveniles, 35.9–44.5 mm SL) Reserva Natural de Tambopata, Laguna Chica, end opposite boat dock (farthest from trail leading to lodge); USNM 302696 (6 ♀ + 1 ♂, 2 cs, 40.3–68.1 mm SL) Prov. Manú, Coche Salvador, and oxbow lake off Río Manú about 1 hr. downriver from Pakitsa; USNM 327324 (3 ♀, 50.0–56.5 mm SL) Prov.Manú, Parque Nacional Manú, Cocha Salvador; USNM 327333 (1 ♀ + 1 ♂, 49.4–71.2 mm SL) Prov. Manú, Parque Nacional Manú, Cocha Nueva; USNM 327334 (2, 58.3–63.5 mm SL) Prov. Manú, Parque Nacional Manú, Río Manú, Cocha Juárez; USNM 327340 (1 ♀ + 1 ♂, 48.8–55.0 mm SL) Prov. Manú, Parque Nacional Manú, Cocha Nueva. Ucayali: MHNG 2407.97 (2 ♀, 68.8–76.0 mm SL) Bagazan, Río Ucayali, Pucallpa; MUSM 10476 (2 ♀, 44.6–47.6 mm SL) Purús, Río Purús, Cocha Zapote; MUSM 10521 (10 ♀ + 5 ♂, 44.7–77.1 mm SL) Purús, Río Purús, Cocha Bola de Oro; USNM 384194 (1 ♀, 44.8 mm SL) Río Purús.

Diagnosis

Hypoptopoma incognitum is distinguished from all congeners, with the exception of H. elongatum, by the presence of a patch of odontodes on the anterolateral surface of the cleithrum at the opening to the branchial chamber. Hypoptopoma incognitum is distinguished from H. elongatum by having a shorter caudal peduncle (caudal-peduncle length 26.0–36.0 (32.0) vs. 32.3–36.3 (34.4); t-test, p < 0.001) (fig. 37); by a deeper, more robust caudal peduncle (caudal-peduncle depth 8.8–11.0 (10.1) vs. 7.9–8.8 (8.4); t-test, p < 0.001); by the round to slightly acute snout (vs. snout appearing pointed due to slight lateral inflexion between rostral plate and first infraorbital); by fewer plates along medial series (21–22 (22) vs. 23); by having caudal-fin lobes light brown (vs. caudal-fin lobes dark).

Fig. 37

Covariation between caudal-peduncle length and standard length for H. elongatum (dots) and H. incognitum (squares).

Description

Morphometric and meristic data presented in table 13. Body robust; greatest body depth at dorsal-fin origin. Dorsal profile of head and body straight from tip of snout to dorsal-fin origin, slightly elevated at posterior supraoccipital tip; straight from dorsal-fin origin to anteriormost procurrent caudal-fin ray. Ventral profile slightly convex from tip of snout to anteriormost procurrent caudal-fin ray. Head moderately depressed, almost as wide as cleithral width; lateral process of lateral ethmoid bone visible dorsally. Snout rounded to slightly acute in dorsal view; dorsally, slightly concave anterior to naris. Posterior surface of bony pit of nasal organ sharply inclined. Trunk cross section between pectoral- and pelvic-fin origin slightly triangular, ovoid to progressively rounded posterior to dorsal fin, progressively compressed posterior to adipose-fin base.

Eyes relatively large, positioned closer to posterior tip of compound pterotic than to tip of snout. Ventral margin of orbit located on ventral surface of head. Dorsal interorbital distance/ventral interorbital distance ratio changing from <1 to >1 during ontogeny.

Total plates in lateral medial series 21–22 (22). Dorsal series plates 19; middorsal series plates 4; midventral series plates 12–14 (13), three plates anterior to first ventral series plate; ventral series plates 19. Second plate of midventral series contacting two plates of medial series.

Abdomen covered by paired series of lateral sickle-shaped plates, with unequal number of plates between left and right sides, 4–8 each; anterior azygous plate usually present; medial abdominal plates, if present, not forming well-defined series. Single anal plate present. Thoracic plates present, 2–6 (4). Preopercular canal in preopercle present, semicircular; anteriormost pore opening between ventral canal-bearing plate and fourth infraorbital; framed by notch at posterolateral margin of canal-bearing plate and ventral margin of fourth infraorbital.

Small odontodes evenly distributed on head. Odontodes along anterior snout margin not arranged in well-defined series, without odontode-free discontinuity between ventrad and dorsad odontodes. Odontodes along dorsal snout margin small, slightly larger than those on dorsal surface of head. Lamina of trunk plates with odontodes arranged in longitudinal rows, becoming progressively smoother ontogenetically; marginal odontodes present in mature adults. Patch of odontodes on anterolateral surface of cleithrum, at opening to branchial chamber, visible upon retraction of branchiostegal membrane. Odontode patch variably developed, from few odontodes to elevated patch of closely arranged odontodes; expression of patch often bilaterally variable.

Total vertebrae 26. Premaxillary teeth 18–23 (21); dentary teeth 17–20 (18). Maxillary barbels short, extended slightly beyond anterior margin of ventral canal-bearing plate in adults.

Dorsal-fin origin located slightly posterior to vertical through pelvic-fin origin. Depressed pectoral fin reaching to anus; pectoral-fin spine with serrae along posterior margin, individual serrae oriented orthogonal to spine shaft. Extension of serrae along pectoral spine margin reduced ontogenetically from proximal two-thirds in smaller specimens to middle third in larger specimens. Pectoral fin reaching to vertical through midpoint between pelvic-fin tip and anal-fin origin. Pelvic fin short with unbranched and first branched rays equal in length. Depressed fin reaching beyond anus, not reaching to anal-fin origin. Caudal-fin margin concave to forked; upper and lower lobes equal. Adipose fin present or absent; when present, composed of bony spine shaft and membrane; when absent, small platelike scar visible.

Color in alcohol

Ground color tan and pale ochre. Melanophores light to dark brown on trunk; melanophores on head and trunk varying from uniformerly distributed to clustered in beanlike spots; melanophores slightly more concentrated along narrow area between compound pterotic, cleithral process, and anterior margin of opercle, at base of dorsal and pectoral fins, and on anterior surface of lip. Deep-lying melanophores arranged in series of blotches posterior to dorsal-fin base. Midlateral stripe situated mostly along medial plates series. Ventral surface of body mostly unpigmented except for scattered melanophores on posterior portion of trunk, anterolateral margin of cleithra, cleithral process, canal-bearing plates, and lateral portions of lateral abdominal series. Paired, dorsal and anal fins with dark brown bands. Dorsal fin with dark triangular spot extended over base of anterior 3–4 branched rays. Series of lanceolate plates at caudal-fin base darkened by black melanophores. Basal triangular spot on caudal fin variably present, typically absent. Caudal fin pigmentation pattern typically composed of three broad bands, with distal tip of lobes light brown. Juveniles up to around 60 mm SL with slightly different caudal-fin pigmentation, having a small triangular spot at base of lower lobe, followed by darker broad bar and darker tips of dorsal and ventral lobes.

Sexual dimorphism

Male urogenital papilla well developed, pointed, joined at base to anterior flaplike anus. Males with patch of tightly arranged small odontodes oriented as a swirl, variably covering first to fourth plates of ventral series, lateral to urogenital papilla. Female anus tubular, without separate urogenital papilla. In females, size and arrangement of odontodes on plates lateral to anus similar to adjacent plates, without distinct patch of differentially arranged odontodes.

Comparisons

The overall pattern of morphometric variation between Hypoptopoma incognitum and H. elongatum is summarized by the results of a sheared principal component analysis on 20 morphometric characters (fig. 38; table 14). The second and third components represent 35.1% and 1.6% of the variation of the morphometric data, respectively; the separation between species is complete along PC2. The analysis shows that the morphometric variance is expressed mostly by variables related to the elongation of the body (trunk and caudal peduncle length, caudal-peduncle depth, and snout length).

Fig. 38

Plot of scores along sheared second and third principal components from the morphometric analysis of body shape between H. elongatum (squares) and H. incognitum (circles).

TABLE 14

Sheared Principal Components Loadings from the Morphometric Analysis of Head and Trunk of Hypoptopoma elongatum and H. incognitum

Distribution

Broadest distribution among species of Hypoptopoma across the central and lower Rio Amazonas basin. It is found in the Rio Tocantins basin and is the only species known for northeastern coastal rivers (fig. 39).

Fig. 39

Drainage map of South America and distribution of H. incognitum (dots), H. gulare (squares), and H. machadoi (triangles). Open symbols designate type localities; some symbols represent more than one locality record.

Etymology

The specific epithet incognitum (Lt. incognitus, meaning “unknown, strange”) is a reference to the fact that specimens of the species have long been misidentified with other species of Hypoptopoma.

Fig. 40

Hypoptopoma steindachneri, holotype by original designation of Boulenger (1895), based on description and illustration appearing in Steindachner NMW 46272, 66.3 mm SL, in dorsal, lateral, and ventral views.

TABLE 15

Morphometric and Meristic Data for Hypoptopoma steindachneri Nontypes: CAS 133271; INHS 39965, 40171, 53744; SIUC 67365; USNM 124286, 190319.

Holotype

Specimen illustrated and described in Steindachner (1879: Taf. 6, fig. 1, 1a, 1b), by original designation of Boulenger 1895: 526. Stated type locality: Rio Amazonas drainage in the delta of the Rio Negro.

Other Material Examined

Brazil, Amazonas: MNRJ 3672 (1 ♀, 84.9 mm SL) Rio Javari (tributary of Rio Solimões) at Benjamin Constant; MZUSP 36204 (1 ♂, 85.1 mm SL) San Antonio do Iça, Rio Solimões; MZUSP 36205 (1 ♀, 82.9 mm SL) Rio Solimões, Ihla Xibeco; MZUSP 36218 (1 ♀ + 1 ♂, 64.6–89.0 mm SL) Campina, Rio Purus. Colombia, Leticia: USNM 190319 (1 ♀ + 1 ♂, 88.4–89.7 mm SL) Leticia. Peru, Loreto: ANSP 182723 (1 ♀, 64.4 mm SL) Río Itaya, ca. 100 minutes upstream from Puerto Belen, Iquitos, by canoe; CAS 133271 (1 ♂, 84.6 mm SL) Río Ampiyacu; INHS 39965 (5 ♀ + 1 ♂, 62.0–98.2 mm SL) Río Itaya, ca. 4–5 km upstream from Iquitos, above and below mouth of Quebrada Mazana; INHS 40171 (1 ♀, 77.3 mm SL) Río Orosa, mouth of Tonche Caño, Madre Selva II field station, 69.4 mi E Iquitos; INHS 53744 (2 ♀, 70.7–88.8 mm SL) Río Nanay, 4.54 km W center of Iquitos; USNM 124826 (1 ♂, 86.3 mm SL) Ampiyacu river; SIUC 67365 (4 ♀ + 3 ♂, 73.1–93.6 mm SL) Río Itaya, upriver of Belen, approx. 4.5 km.

Diagnosis

Hypoptopoma steindachneri is distinguished from all congeners by the presence of two or more paranasal plates between the pararostral plates and the second infraorbital (fig. 7C) (vs. a single paranasal plate in H. gulare (fig. 7B) and H. machadoi, or paranasal plates absent (fig. 7A) in all other Hypoptopoma species); by having a single plate between the canal-bearing plate and the first, second, and third infraorbitals (fig. 5B) (vs. two plates); by having the canal-bearing plate subdivided into a smaller plate along the anteromedial margin and the larger posterior portion that bears the canal (fig 5B) (vs. a single, undivided canal-bearing plate); by having the basipterygium constricted laterally (interpelvic distance 2.0–6.4 (5.1) vs. interpelvic distance > 6.5) (fig. 41B); by having the anterodorsal basipterygium lamina that forms the channel for the pelvic arrector muscles extended anteriorly beyond the lateral basipteryigium process (vs. anterodorsal basipterygium lamina not extended beyond the lateral basipterygium process); by having the tips of the caudal-fin rays darkly pigmented, forming a vertical band along the fin margin (vs. tips of the caudal-fin rays not uniformly dark, not forming a vertical band along posterior margin). Hypoptopoma steindachneri is further distinguished from all congeners, except for H. brevirostratum, by the presence in mature males of a membranous outgrowth between pelvic spine and first pelvic-fin branched ray (vs. membranous outgrowth absent).

Fig. 41

Basipterygium, ventral view, anterior toward top. A, H. incognitum; B, H. steindachneri.

Description

Morphometric and meristic data presented in table 15. Body robust; greatest body depth at dorsal-fin origin (fig. 42). Dorsal profile of head concave from tip of snout to frontals, convex from that point to dorsal-fin origin; roughly straight from dorsal-fin origin to anteriormost procurrent caudal-fin ray. Ventral profile smoothly convex from tip of snout to anteriormost caudal-fin procurrent ray. Head strongly depressed anterior to orbits, as wide as cleithral width; lateral process of lateral ethmoid bone visible dorsally. Snout rounded; flattened anterior to naris. Posterior surface of bony pit of nasal organ sharply inclined. Body cross section between pectoral- and pelvic-fin origins slightly triangular, round to progressively compressed posterior to dorsal fin.

Fig. 42

Hypoptopoma steindachneri, SIUC 29198, 88.9 mm female, in dorsal, lateral, and ventral views.

Eyes relatively large, positioned slightly closer to posterior tip of compound pterotic than to tip of snout. Ventral margin of orbit located on ventral surface of head. Dorsal interorbital distance greater than ventral interorbital distance.

Total plates in lateral medial series typically 22. Dorsal series plates 19–20 (19); middorsal series plates 3–4 (4); midventral series plates 13–15 (15), three plates anterior to first ventral series plate; ventral series plates 19–20 (19). Second plate of midventral series contacting two plates of medial series.

Abdomen covered by paired series of lateral sickle-shaped plates, with unequal number of plates between left and right sides, 3–8 each; anterior azygous plate usually present. Single anal plate. Thoracic plates present, 2–6. Canal in preopercle present, semicircular; anterior pore located between ventral canal-bearing plate and fourth infraorbital, framed by notch at posterolateral margin of canal-bearing plate and ventral margin of fourth infraorbital, notch with greater contribution from fourth infraorbital.

Small odontodes evenly distributed on head. Odontodes on rostral margin of snout not arranged in well-defined series, without odontode-free discontinuity between ventrad and dorsad odontodes. Odontodes along dorsal rostral margin small, only slightly larger than those on head. Lamina of trunk plates with odontodes arranged in longitudinal rows, becoming progressively smoother ontogenetically; marginal odontodes well developed.

Total vertebrae 26. Premaxillary teeth 15–21 (19); dentary teeth 13–20 (16). Maxillary barbels short; in adults extending slightly beyond anterior margin of ventral canal-bearing plate.

Dorsal-fin origin located slightly anterior to vertical through pelvic-fin origin; depressed dorsal fin reaching almost to vertical through posterior tip of anal fin. Pectoral fin variably reaching to anal-fin origin. Pectoral spine serrae orthogonal to spine shaft, typically entirely reduced. Pelvic fin short, unbranched and first branched rays of equal length, pelvic fin reaching to anus, not reaching anal-fin origin. Caudal-fin margin concave to forked; upper and lower lobes equal. Adipose fin variably present; when present, consisting of small plate with few small odontodes.

Color in alcohol

Ground color tan and pale ochre. Melanophores light to dark brown; arranged in clusters on trunk and at base of plates yielding mottled appearance. Pigmentation on head more uniformly distributed; melanophores slightly more concentrated on frontals, narrow area along anterior margin of opercle, narrow band along margin of snout slightly reflected ventrally. Deep-lying melanophores arranged in series of blotches posterior to dorsal-fin base and lateral stripe on body mostly along trunk medial series of plates. Ventral surface of body mostly unpigmented except for scattered melanophores on posterior portion of trunk region. Paired fins with faint bands. Unpaired fins with dark brown bands. Dorsal fin with dark triangular spot extended over base of branched rays. Basal plates of caudal fin with pigmented spot of black melanophores, contiguous to basal dark band, extended along one-fourth length of branched rays. Distal tips of unbranched and branched caudal-fin rays dark, forming continuous narrow band (fig. 17E).

Sexual dimorphism

Male urogenital papilla pointed, variably joined to anterior flaplike anus. Males with patch of tightly arranged small odontodes oriented as a swirl, variably covering first to fourth plates of ventral series, lateral to urogenital papilla. Female anus tubular, without separate urogenital papilla. In females, size and arrangement of odontodes on plates lateral to anus similar to adjacent plates, without distinct patch of differentially arranged odontodes.

Distribution

Known from tributaries of the lower Rio Ucayali and Rio Solimões basin (fig. 32).

Taxonomic remarks

The species herein designated as Hypoptopoma steindachneri is remarkable in possessing a large number of unique autapomorphic morphological characters serving to diagnose the species among congeners. Boulenger (1895) established Hypoptopoma steindachneri on the basis of the illustration of a single specimen that Steindachner (1879) had identified as H. thoracatum. Boulenger's H. steindachneri has been available since then, although without formal designation of a type specimen. Schaefer (1996b) subsequently argued that the specimen NMW 46272 should be regarded as the holotype of H. steindachneri. The specimen, labeled as H. thoracatum, had catalog date of entry of 1874 (“Brazil, Río Negro Mündg.”) and showed similar values for a series of morphometric characters used in the Steindachner (1879) description. Schaefer (1996b) indicated that the differences in the pattern of plate distribution and the pectoral-fin length observed between the specimen illustrated by Steindachner (1879) and NMW 46272 were due to inaccuracy in the illustration. Subsequent examination of additional material has led us to the conclusion that those supposed discrepancies in plate-related characters and body robustness are rather consistent across material identified as H. steindachneri from throughout its geographic range. The following characters are shared by the specimen illustrated by Steindachner and 25 specimens (62.0–98.2 mm SL) we examined, but not shared by specimen NMW 46272: (1) presence of more than one paranasal plates; (2) paranasal plates separating second infraorbital bone from series of pararostral plates; (3) ventral canal-bearing plate subdivided; (4) one dermal plate laterally contacting first, second, and third infraorbital bones, and mesially contacting mostly the anteriormost subdivision of the ventral canal-bearing plate; (5) basipterygium laterally constricted, with interpelvic distance 4.5%–6.4% SL; body robust, which is reflected by the morphometric characters caudal-fin base depth (10.0% SL), cleithral width (27.2% SL), least orbit/naris distance (6.7% SL), and (9) adipose fin absent. Consequently, the designation of NMW 46272 as holotype of H. steindachneri is herein invalidated. Instead, we argue that the single specimen illustrated by Steindachner (1879) is the holotype by original designation of Boulenger (1895), as per application of ICZN art. 73.1.4 (ICZN, 1999), regardless of whether the holotype no longer exists.

Comparisons

Our observations confirmed H. steindachneri as a separate species from H. gulare. Hypoptopoma steindachneri is distinguished from H. gulare, in addition to the character presence of typically more than one paranasal plates between the second infraorbital and the nasal organ (vs. presence of a single paranasal plate), by having a wider head (head width 25.4–28.0 (26.3) vs. 22.4–24.2 (23.4); t_(14,247), p < 0.001), longer least distance between orbit and naris (least orbit/nare distance 6.2–7.6 (7.1) vs. 4.7–6.0 (5.3); t_(17,720), p < 0.001), and deeper caudal peduncle (caudal-peduncle depth 9.7–11.3 (10.8) vs. 7.2–9.1 (8.3); t_(11.321), p < 0.001); by having the second infraorbital entirely separated from the pararostral plates (fig. 7C) (vs. second infraorbital in contact with the pararostral plates); by having the canal-bearing plate typically subdivided (vs. ventral canal-bearing plate undivided); by having the tips of all caudal-fin branched rays typically pigmented (vs. middle caudal-fin branched rays distally light); and by the presence in males of a well-developed flap of soft tissue along the posterior surface of the pelvic spine (vs. absence in males of a flap of soft tissue along the posterior surface of the pelvic spine).

Fig. 43

Hypoptopoma gulare, holotype, ANSP 21477, 81.9 mm SL, male, in dorsal, lateral, and ventral views.

TABLE 16

Morphometric and Meristic Data for Hypoptopoma gulare Holotype: ANSP 21477. Nontypes: INHS 101387; MUSM 4183; NRM 57231; SIUC 26798.

Holotype

ANSP 21477, 81.9 mm SL, ♂, Peru: Loreto, Peruvian Amazonia, Río Marañón; collected by J. Orton, 1877.

Other Material Examined

Peru, Amazonas: LACM 36333-3 (1 ♀ + 1 ♂, 55.1–63.1 mm SL) Quebrada Caterpiza. Loreto: CAS 77138 (1 ♀, 76.7 mm SL) Ucayali, Lago Cashiboya, a cutoff lake of Río Ucayali above Contamana; CAS 77139 (1 ♀, 56.2 mm SL) Río Pacaya, at the mouth, Bretaña; FMNH 92883 (1 ♀, 78.3 mm SL) Yanamono creek and the small tributary behind Travelrama lodge; FMNH 92884 (1 ♀, 66.1 mm SL) swampy area in the interior of small island in the Río Amazonas; FMNH 108759 (19 ♀ + 10 ♂, 58.9–80.9 mm SL) Río Marañón dr., Caño Abico, tributary to Río Samiría, ca. 6–7 km from mouth in Río Marañón; FMNH 108760 (1 ♀, 33.6 mm SL) Río Marañón dr., Punto Caño ca. 7 km above mouth of Río Chambira in Río Marañón; INHS 40008 (1 ♀, 70.4 mm SL) Río Amazonas dr., Río Orosa, Caño Zapatilla, ca. 10 min. upstream by boat from Río Orosa, 76.4 mi E Iquitos; INHS 40216 (5 ♂, 75.7–87.0 mm SL) Río Itaya dr., Quebrada Mazama, ca. 1 km upstream from confluence with Río Itaya, S of Belem (Iquitos); INHS 44124 (2 ♀, 52.2–58.5 mm SL) Río Amazonas dr., Río Napo and Quebrada Mazán, 33.3 km NE Iquitos; INHS 52027 (1 ♀, 53.1 mm SL) Río Amazonas dr., Río Itaya, Moena caño near confluence with Ullpa caño and lower Ullpa caño, SE of Iquitos; INHS 53742 (2 ♀ + 1 ♂, 71.6–88.1 mm SL) Río Amazonas dr., Río Pampa Chica, 4.5 km W center of Iquitos; INHS 53845 (2 ♀ + 2 ♂, 76.7–105.0 mm SL) Río Amazonas dr., Río Napo, opposite Mazán, N channel Río Napo, N of Isla Milagro; INHS 101387 (63 ♀ + 47 ♂, 46.8–88.4 mm SL) Río Amazonas dr., Río Yamashi, Yamashi, 69.8 mi. E Iquitos; INHS 101390 (2 ♂, 68.5–81.0 mm SL) Río Amazonas dr., Río Orosa, mouth of Tonche Caño, Madre Selva II field station, 69.4 mi E Iquitos; MHNG 2390.25 (1 ♀, 44.5 mm SL) Río Ucayali, San Antonio; MUSM 2673 (12 ♀ + 2 ♂, 63.9–79.8 mm SL) Maynas, Iquitos, Cocha Aguajal; MUSM 7298 (1 ♀, 37.4 mm SL) Alto Amazonas, Río Pastaza, Lago Rimachi, Quebrada Chapuli; MZUSP 15308 (1 ♀, 86.2 mm SL) Río Corrientes; MZUSP 36206 (1 ♂, 43.2 mm SL) Río Ucayali; MZUSP 36208 (1 ♀, 43.0 mm SL) Río Ucayali, Sgto. Lores; SIUC 28113 (1 ♀, 39.0 mm SL) Río Napo, confluence with Río Mazán, ca. 2–3 km N town of Mazán; SU 33272 (1 ♂, 42.6 mm SL) Río Ampiyacu; NRM 17988 (2 ♀, 31.5–78.4 mm SL) Río Napo dr., Cayapoza, small laguna on left bank island; NRM 47513 (3 ♀, 45.7–48.7 mm SL) Río Samiria dr., caño Atún; NRM 57231 (13 ♀ + 4 ♂, 2 cs, 59.6–85.5 mm SL) Río Tahuayo dr., Caño Huayti; SIUC 26798 (1 ♀ + 1 ♂, 57.6–82.1 mm SL) Prov. Fernando Lores, Lago Aguajal, Lucero Pata (between Iquitos and Nauta); SIUC 29198 (2 ♂, 85.1–88.8 mm SL) Prov. Maynas, Río Itaya, upriver of Belén, approx. 4.5 km; SIUC 29363 (1 ♀, 51.5 mm SL) Río Napo, Mazán, 33.3 km from center of Iquitos; SIUC 29422 (2 ♀, 60.1–71.9 mm SL) Itaya dr., Ushpa caño, ca. 100 yrs. uptream from confluence with caño Moena; SIUC 29646 (1 ♀, 71.3 mm SL) Río Nanay, Pampachica beach, 4.5 km from Iquitos center; SIUC 29664 (1 ♂, 76.9 mm SL) Río Napo, backwater playa behind Isla Milagro, 1.03 km from Mazán; SIUC 30062 (1 ♀, 60.2 mm SL) Prov. Maynas, Río Itaya and Quebrada Mazán, 11 km from Iquitos center; SIUC 67364 (2 ♀, 40.3–59.4 mm SL) Río Napo, confluence with Río Mazán, ca. 2–3 km N (town of) Mazán; SU 34253 (1 ♀, 89.6 mm SL) Río Ampiyacu near Pebas. Ucayali: FMNH 42963 (2 ♀, 63.5–77.9 mm SL) Yarinacocha, Río Ucayali dr., Pucallpa. MHNG 2618.88 (2 ♀, 60.2–72.6 mm SL) Pucallpa, Tapistica Alejandria; MHNG 2389–60 (1 ♀ + 1 ♂, 74.1–76.5 mm SL) Pucallpa, Río Ucayali, Romainecocha; MHNG 2389-62 (3 ♀, 56.6–72.9 mm SL) Pucallpa, Río Ucayali, Yarinacocha; MHNG 2618.86 (1 ♀, 70.0 mm SL) Pucallpa, San Antonio, Río Ucayali; MHNG 2618.87 (2 ♀, 68.8–76.0 mm SL) Pucallpa, Bagazán, Río Ucayali; MUSM 1845 (10 ♀ + 2 ♂, 57.28–77.10 mm SL) Pucallpa, Coronel Portillo, Tapistica Alejandria; MUSM 4183 (7 ♀ + 1 ♂, 55.7–80.0 mm SL) Pucallpa, Coronel Portillo, Río Ucayali, Cocha Tacshitea; MZUSP 36195 (21 ♀ + 3 ♂, 55.2–77.4 mm SL) Pucallpa, Río Ucayali; MZUSP 36196 (2 ♀, 52.9–61.0 mm SL) Pucallpa, Río Ucayali; MZUSP 36199 (4 ♀ + 8 ♂, 58.0–76.9 mm SL) Pucallpa, Cocha Romaine, Río Ucayali; MZUSP 36200 (1 ♂, 70.7 mm SL) Pucallpa, Laguna Yarinacocha; MZUSP 36201 (1 ♂, 69.4 mm SL) Laguna Yarinacocha, Río Ucayali, close to Pucallpa; MZUSP 36202 (1 unsexed, 55.1 mm SL) Pucallpa, Río Ucayali; MZUSP 36207 (1 ♀, 42.03 mm SL) Laguna Yarinacocha, Río Ucayali; MZUSP 36229 (2 ♀, 54.5–59.6 mm SL) Utuquinia, Río Ucayali; USNM 284866 (10 ♀, 48.9–60.8 mm SL) Coronel Portillo, Yarinacocha, side caño. Brazil, Acre: MZUSP 50368 (1 ♀, 70.0 mm SL) Lago do Breu, Ponto 7, Rio Jurúa. Amazonas: INPA 2420 (17 ♀ + 9 ♂, 62.2–85.6 mm SL) Paraná Jaraná, Río Japurá; INPA 2489 (1 ♀, 78.8 mm SL) Lago do Reis; MNHN A-1966 (73.7 mm SL) (holotype of Otocinclus joberti Vaillant 1880) Calderon; MZUSP 36209 (6 ♀ + 6 ♂, 55.1–72.9 mm SL) Lago Supiá, in front of Codajás. Colombia, Amazonas: NRM 16561 (1 ♀ + 2 ♂, 77.9–82.5 mm SL) Leticia, lagos de Leticia.

Diagnosis

Hypoptopoma gulare is distinguished from all congeners, with the exception of H. machadoi, by the presence of a single paranasal plate separating the lateral process of the lateral ethmoid from the second infraorbital and the nasal organ (fig. 7B). In contrast, in all other species of Hypoptopoma, except H. steindachneri, the paranasal plates are absent and the lateral process of the lateral ethmoid contacts the second infraorbital (fig. 7A). In H. steindachneri, there are two or more paranasal plates. Hypoptopoma gulare is distinguished from H. machadoi by a slender caudal peduncle (caudal-peduncle depth 7.2–9.1 (8.3) vs. 9.0–12.0 (10.3); t_(16.298), p < 0.001); by fewer premaxillary (12–16 (14) vs. 16–25 (20); t_(12,675), p < 0.001) and dentary teeth (10–14 (12) vs. 14–21 (17); t_(12,068), p < 0.001); by lanceolate plates at the base of the caudal fin with dark spot, asymmetrically shaped and slightly more extended over lower-lobe branched rays, followed by two V-shaped bars pointing forward, with the anterior bar variably developed on the upper lobe but always connected at its angle with the basal spot (vs. the lanceolate plates at the base of the caudal fin with a light brown spot, symmetrically shaped and shortly extended over the branched rays, typically followed by three vertical bands variably defined, with the anterior band not continuous in the middle with the basal spot); by dorsal fin with dark brown, roughly triangular spot extended over base of anterior 3–4 branched rays, followed typically by 2–3 bars (vs. dorsal fin without triangular spot at base; dorsal fin typically with 4–7 bars).

Description

Morphometric and meristic data presented in table 16. Body robust; greatest body depth at dorsal-fin origin. Dorsal profile of head and body straight from tip of snout to dorsal-fin origin, slightly angled dorsally at posterior tip of supraoccipital; straight from dorsal-fin origin to anteriormost procurrent caudal-fin ray. Ventral profile straight from tip of snout to anteriormost procurrent caudal-fin ray. Head moderately depressed, almost as wide as cleithral width; lateral process of lateral ethmoid visible dorsally. Snout rounded to slightly acute in dorsal view; slightly concave dorsally anterior to naris. Posterior surface of bony pit of nasal organ sharply inclined. Trunk cross section between pectoral- and pelvic-fin origins slightly triangular, ovoid to progressively rounded posterior to dorsal fin, progressively compressed posterior to adipose-fin base.

Eyes relatively large, positioned closer to posterior tip of compound pterotic than to tip of snout. Ventral margin of orbit located on ventral surface of head. Dorsal interorbital distance/ventral interorbital distance ratio changing from <1 to >1 during ontogeny.

Total plates in medial series 22–23 (22). Dorsal series plates 19–20 (19); middorsal series plates 4; midventral series plates 12–13 (13), three plates anterior to first ventral series plate; ventral series plates 19–20 (19). Second plate of midventral series contacting two plates of medial series.

Abdomen covered by paired series of lateral sickle-shaped plates, with unequal number of plates between left and right sides, 4–8 each; anterior azygous plate usually present; medial abdominal plates, if present (22% of 132 individuals examined), not forming well-defined series. Single anal plate present. Thoracic plates present, 2–6. Preopercular canal present and semicircular; anteriormost pore opening between ventral canal-bearing plate and fourth infraorbital; posterolateral margin of canal-bearing plate and lateral margin of fourth infraorbital smooth, framed by notch at posterolateral margin of canal-bearing plate and ventral margin of fourth infraorbital.

Small odontodes evenly distributed on head. Odontodes along snout margin not arranged in well-defined series, without odontode-free discontinuity between ventrad and dorsad odontodes. Odontodes on dorsal snout margin small, slightly larger than those on dorsal surface of head. Lamina of trunk plates with odontodes arranged in longitudinal rows, becoming progressively smoother ontogenetically; marginal odontodes present in mature adults.

Total vertebrae 26. Premaxillary teeth 12–16 (10); dentary teeth 10–14 (10). Maxillary barbels short, reaching slightly beyond anterior margin of canal-bearing plate in adults.

Dorsal-fin origin located slightly posterior to vertical through pelvic-fin origin. Depressed dorsal fin reaching to vertical through midpoint of anal-fin base. Pectoral fin reaching to vertical through midpoint between pelvic-fin tip and anal-fin origin. Pectoral spine serrae present, oriented orthogonal to spine shaft. Extension of serrae along pectoral spine margin reduced ontogenetically from proximal two-thirds in smaller specimens to middle third in larger specimens. Pelvic fin short, unbranched and first branched rays of equal length. Depressed fin reaching anus, not reaching anal-fin origin. Caudal-fin margin concave to forked; upper and lower lobes equal. Adipose fin present.

Color in alcohol

Ground color tan and pale ochre. Melanophores light to dark brown on trunk and particularly clustered at base of plates, resulting in mottled appearance; melanophores on head more uniformly distributed; melanophores slightly more concentrated along narrow area among compound pterotic, cleithral process, and opercle, at base of dorsal and pectoral fins, and on anterior surface of lip. Deep-lying melanophores arranged in series of blotches posterior of dorsal-fin base. Midlateral stripe situated mostly along medial series of trunk plates. Ventral surface of body mostly unpigmented except for scattered melanophores on posterior portion of trunk, anterolateral margin of cleithra and posterior tip of cleithral processes, ventral canal-bearing plates, and lateral portions of lateral abdominal series. Paired dorsal and anal fins with dark brown bars, roughly orthogonal to rays. Dorsal fin with dark brown, roughly triangular spot extended over base of anterior 3–4 branched rays. Series of lanceolate plates at base of caudal fin darkened by black melanophores. Basal triangular dark spot over caudal-fin lower lobe determined by lower-lobe arm of most anterior V-shaped bar variably merging with spot at lanceolate plates. Upper-lobe arm of same bar light brown to absent, clearly separated from spot at lanceolate plates. One or two following, nearly complete V-shaped bars pointing forward and 1–3 incomplete bars along posterior half of upper and lower lobes; tip of branched rays usually light (fig. 17D).

Sexual dimorphism

Males with urogenital papilla well developed, pointed; joined at base to anterior flaplike anus. Males with patch of tightly arranged small odontodes oriented as a swirl, variably covering from first to fourth plates of ventral series, lateral to urogenital papilla and narrow band along posterior border of anal plate. Female anus tubular, without separate urogenital papilla. In females, size and arrangement of odontodes on plates lateral to anus similar to adjacent plates, without distinct patch of differentially arranged odontodes.

Distribution

Upper Amazon River in Brazil; lower and upper Río Ucayali (fig. 39).

Taxonomic Remarks

Cope (1878) described Hypoptopoma gulare based on a single specimen collected in 1877 near Pebas by Orton. Cope compared the new species with H. bilobatum Cope (1870) and distinguished H. gulare by having a more robust body, a lower number of lateral plates, presence of thoracic plates, and the absence of a medial series of abdominal plates. Vaillant (1880) described the new species Otocinclus joberti based on the examination of a single specimen collected by Jobert in Calderón (Rio Amazonas, Manaus region). The genus Otocinclus had been established by Cope (1871) (for a historical review, see Schaefer, 1997). Vaillant failed to recognize the similarity between his specimen and previously described Hypoptopoma species (H. thoracatum in 1868, H. bilobatum in 1870, and H. gulare in 1878). Berg (1898) properly reassigned Vaillant's species to the genus Hypoptopoma. Gosline (1945) proposed H. joberti as a junior synonym of H. gulare, an opinion shared by Fowler (1954); however, neither of these authors provided argumentation for that nomenclatural act. Our examination of the type specimens and additional comparative material confirm the synonymy of H. joberti and H. gulare.

Fig. 44

Hypoptopoma machadoi, paratype, AMNH 77794, 46.2 mm SL female, in dorsal, lateral, and ventral views.

TABLE 17

Morphometric and Meristic Data for Hypoptopoma machadoi Holotype: MBUCV V-35362. Paratype: AMMH 77794. Nontypes: ANSP 165843; CAS 64283; FMNH 85814, 85826; LACM 43204-4; MCNG 9369.

Holotype

MBUCV V-35362 (♀, 46.2 mm SL) Venezuela: San Fernando de Apure, swamps on south bank of Río Apure, ca. 3 km west of Fisheries Station; collected by Apure Fisheries Station technicians, 21 January 1983.

Paratypes

AMNH 77794, 23 females, 42.1–53.7 mm SL (collected with holotype).

Other Material Examined

Colombia, Meta: ANSP 128569 (1 ♂, 48.3 mm SL) Hacienda Mozambique, N. shore at main house; ANSP 128955 (9 ♀ + 3 ♂, 45.8–61.7 mm SL) Río Negro, just downstream from where it passes under the main Villavicencio, Puerto López highway at La Balsa (W side of river); ANSP 128956 (6 ♀ + 3 ♂, 50.4–69.3 mm SL) Río Negrito midway between La Argelia and La Balsa (Plancha 267 – Río Guayuriba); ANSP 128960 (16 ♀ + 2 ♂, 47.5–66.5 mm SL) Río Negro, just downstream from where it passes under the main Villavicencio, Puerto López highway at La Balsa; ANSP 131666 (5 ♀ + 1 ♂, 45.6–61.9 mm SL) Río Negrito downstream bridge at La Balsa; ANSP 134438 (18 ♀ + 3 ♂, 2 cs, 39.8–53.2 mm SL) tributary caño La Raya (first caño N de La Siberia); ANSP 139463 (3 juveniles, 25.5–31.0 mm SL) canal y laguna Aerotas, S. side of Río Metica, entrance on Metica, ca. 2 km. SW (upstream) of entrance to Lake Mozambique; FMNH 84005 (1 ♂ + 2 juveniles, 24.3–51.3 mm SL) Caño Venturosa, at 1 km N Puerto López. Venezuela, Amazonas: MCNG 6306 (4 ♀, 43.7–59.7 mm SL). Anzoátegui: ANSP 166734 (2 ♀, 54.9–57.8 mm SL) Río Orinoco basin, Soledad, L. Terecaya. Apure: ANSP 130028 (1 ♀, 41.7 mm SL) Camaguán swamp, on W side of Hwy to San Fernando de Apure, about 2 km N of Camaguán; ANSP 130040 (12 ♀, 1 cs; 38.2–50.5 mm SL) S bank and backwater areas pm downstream side of bridge at San Fernando de Apure; ANSP 165843 (4 ♀ + 3 ♂, 53.6–69.0 mm SL) Río Cunaviche, ca. 20 km SW of Cunaviche on San Fernando de Apure–Puerto Paez Hwy; ANSP 165844 (1 ♀, 38.8 mm SL) Río Matiyure, at Achaguas; ANSP 166433 (2 ♀, 31.4–44.9 mm SL) Caño Caicara, 10–12 km W of Montecal; CAS 64271 (3 ♀, 44.0–58.1 mm SL) pool just S of Bruzual alongside dyke that parallels highway behind bull run; CAS 64283 (59 ♀ + 4 ♂, 35.6–62.2 mm SL) Caño first creek S of Bruzual at red steel bridge; FMNH 85814 (35 ♀ + 3 ♂, 33.9–53.4 mm SL) River 24 km S Biruaca on road to San Juan de Apayara; FMNH 85826 (10 ♀ + 1 ♂, 31.2–47.2 mm SL) Río Aruaca, 32.5 Km S Biruaca; INHS 29809 (13 ♀, 40.7–53.2 mm SL) tributary caño Setento, 10 km. S Bruzual; INHS 30098 (34 ♀, 27.9–45.4 mm SL) Caño Guaritico ( =  caño Maporal) (Río Apure drainage), 58 km SSW Bruzual; MCNG 6104 (7 ♀, 37.1–44.3 mm SL); MCNG 9369 (8 ♀ + 4 ♂, 42.5–49.3 mm SL); MZUSP 27973 (51 ♀, 32.3–51.0 mm SL) caño 1 km ao sul passagem de balsa, na altura da estrada de San Fernando de Apure; USNM 257971 (2 ♀, 43.3–44.2 mm SL) Río Apure West of town center; USNM 257972 (68 ♀ + 1 ♂, 35.1–49.7 mm SL) Caño Caicará, where crossed by bridge on road from Montecal; USNM 257975 (2 ♀, 46.8–50.6 mm SL) Río Apure ca. 2 km East of bridge at San Fernando de Apure; USNM 260193 (52 ♀ + 2 ♂, 32.7–66.1 mm SL) side channel of Río Apure ca. 5 km West of San Fernando de Apure. Barinas: FMNH 105985 (2 ♀, 36.7–42.9 mm SL) Río Suripa ca. 10 min. by boat above confluence with Río Carapo; FMNH 105986 (1 ♀, 62.5 mm SL) Río Anaro ca. 10 min. from mouth in Río Suripa, small island and collected small arms of river; FMNH 105987 (27 ♀ + 4 juveniles, 30.7–49.2 mm SL) Caño La Indiecita near mouth in Río Suripa ca. 35 min. up river from boat launch in Hato Mercedes; FMNH 105988 (3 ♀, 42.7–48.1 mm SL) Caño Socopo ca. 3.5 hours upstream from boat launch of Hato Mercedes in Río Suripa.; FMNH 108762 (1 ♀, 48.3 mm SL) Río Orinoco drainage, Caño Caigua ca. 20 min. by boat from boat launch at Hato Las Mercedes; INHS 28696 (20 ♀, 47.1–56.0 mm SL) Río Santo Domingo (Río Apure drainage) in Torunos, hacienda La Isla; MCNG 21329 (7 ♀, 42.2–53.3 mm SL); MCNG 26277 (6 ♀ + 1 ♂, 41.9–55.9 mm SL). Bolívar: ANSP 135631 (11 ♀ + 7 ♂, 42.1–63.1 mm SL) Caño Chuapo ca. 20 min. downstream from Jabillal (opposite bank) on Río Caura; ANSP 135678 (20 ♀ + 1 ♂, 36.8–57.1 mm SL) mouth of caño Chuapo ca. 20 min. downstream from Javillal (opposite bank) on Río Caura; ANSP 139521 (1 ♀, 39.9 mm SL) Quebrada Cuchivero (Cuchiverito), tributary of Río Mato (right bank); ANSP 139620 (12 ♀ + 1 ♂, 40.0–61.2 mm SL) Sandbar along Río Mato; ANSP 160863 (1 ♀, 42.2 mm SL) Río Cuchivero at Cuchivero ferry crossing; FMNH 97050 (1 ♀, 40.8 mm SL) Río Orinoco, cove West end of islote Fejardo, 182 naut. mi. upstream from sea buoy; FMNH 108767 (1 ♀, 43.4 mm SL) Río Orinoco basin, S bank of Río Orinoco at mouth of Río Orocopiche, in mouth and along Orinoco; FMNH 108768 (4 ♀, 38.2–55.0 m SL) Río Orinoco basin, Río Orinoco just above bridge at Ciudad Bolívar; MCNG 6658 (3 ♀ + 1 ♂, 47.4–70.8 mm SL); SU 48664 (9 ♀ + 1 ♂, 40.6–48.9 mm SL) Río Orinoco at Caicará; USNM 265696 (1 ♀, 41.5 mm SL) Río Orinoco, Cove, Islote de Fajardo, 182 naut. mi. upstream from sea buoy; USNM 265963 (1 ♀, 47.6 mm SL) small caño connecting with Río Orinoco immediately South of El Burro. Cojedes: MCNG 13770 (1 ♀ + 6 juveniles, 20.6–45.0 mm SL). Delta Amacuro: AMNH 47955 (6 ♀, 38.6–48.0 mm SL) lagoon at caño Araguaíto, ca. Km 130, Río Orinoco; ANSP 152860 (9 ♀, 1 cs, 36.7–47.1 mm SL) ca. Km. 65, small caño near mouth of caño Fiscal, Río Orinoco; FMNH 97051 (1 ♀, 36.3 mm SL) backwater caño Araguao, 112 naut. mi. upstream from sea buoy; FMNH 97052 (4 ♀, 44.4–49.7 mm SL) Río Orinoco, cave on sand bar near E end of Isla Portuguesa, 117 naut. mi. upstream from sea buoy; FMNH 97066 (14 ♀, 37.9–53.5 mm SL) Río Orinoco, first small caño on W side of caño Paloma 100 m above its mouth, 92 naut. mi. upstream from sea buoy; FMNH 108765 (1 ♀, 43.4 mm SL) Río Orinoco at plays on North side; FMNH 108766 (2 ♀, 44.7–48.3 mm SL) Río Santa Clara at first tributary on East side ca. 0.5 hour above mouth; LACM 43016-2 (1 ♀, 48.2 mm SL) N bank – beach across from Los Castillos; 160 NM upstream from sea buoy; LACM 43151-16 (69 ♀ + 1 ♂, 32.9–54.1 mm SL) Río Orinoco, inlet; 82 NM upstream from sea buoy; LACM 43204-4 (30 ♀ + 3 ♂, 35.2–66.8 mm SL) Río Orinoco, shallow lagoon on N side of river, W of caño Araguarito; LACM 43297-2 (15 ♀ + 1 juvenile, 25.3–46.5 mm SL) Teda, caño Paloma system; USNM 265682 (1 ♀, 44.3 mm SL) Río Orinoco, first small caño on W side of caño Paloma 100 m above its mouth, 92 naut. mi. upstream of sea buoy; USNM 265708 (5 ♀, 38.3–50.6 mm SL) Río Orinoco, small caño near mouth of caño Socoroco, 111 naut. mi. upstream from sea buoy. Guárico: ANSP 166732 (19 ♀, 38.9–48.8 mm SL) Río Orinoco basin, Cabruta, Laguna Larga II; ANSP 166733 (1 ♀ + 1 ♂, 37.4–62.7 mm SL) Río Orinoco basin, Cabruta, Laguna Larga II; FMNH 85807 (1 ♀, 39.9 mm SL) pond by river at 8 km E of Camaguán on road to Uvenito; INHS 62063 (43 ♀,33.9–47.1 mm SL) caño (Río Guariquito–Río Orinoco drainage) 100 air km E San Fernando; MCNG 15072 (10 ♀, 37.8–48.7 mm SL); USNM 257969 (7 ♀, 32.8–43.4 mm SL) Caño Falcon ca. 5 km north of RPV 83-4; Río Portuguesa drainage basin; USNM 257973 (16 ♀, 36.2–48.3 mm SL) Caño to West of highway from Calabozo to San Fernando about 35 km South of Fundo Masaguaral, Caño Falcon; USNM 257976 (1 ♀, 45.6 mm SL) Río Guárico at Flores, Moradas ranch ca. 3–4 km East of road from Calabozo to San Fernando. Monagas: CAS 58157 (5 ♀, 47.0–54.8 mm SL) Río Orinoco, small caño 0.75 miles upstream from mouth of caño Guarguapo, near Barrancas; LACM 43382-29 (7 ♀, 43.0–54.9 mm SL) Río Orinoco, secondary caño about 500 m from its mouth in caño Guarguapo; LACM 43423-4 (31 ♀ + 1 ♂, 35.1–50.7 mm SL) Río Orinoco, S shore of Isla Noina, 51–52 NM from sea buoy; USNM 163172 (1 ♀, 53.0 mm SL) Caicará, Río Guarapiche; USNM 265718 (17 ♀, 3 cs, 36.3–48.3 mm SL) Río Orinoco, 161 naut. mi. upstream from sea buoy, laguna Tapatapa on Isla Tapatapa near downstream end of caño de Limón. Portuguesa: MCNG 1179 (4 ♀ + 3 ♂, 39.0–55.5 mm SL); TNHC 12513 (6, 43.6–53.3 mm SL) Caño Maraca at Urriolas ranch, 35 km SE Guanaré; TNHC 12766 (10 ♀, 35.6–39.8 mm SL) Caño Maraca at Urriolas ranch, 35 km SE Guanaré; USNM 348681 (12 ♀, 38.2–57.8 mm SL) Guanaré-Guanarito, road at road km 60; caño Igues–Río Portuguesa (Caño Maraca).

Diagnosis

Hypoptopoma machadoi is distinguished from all congeners, with the exception of H. gulare, by the presence of a single paranasal plate separating the lateral process of the lateral ethmoid from the second infraorbital and the nasal organ (fig. 7B). In contrast, in all other species of Hypoptopoma, except H. steindachneri, the paranasal plates are absent and the lateral process of the lateral ethmoid contacts the second infraorbital (fig. 7A). In H. steindachneri, there are two or more paranasal plates (fig. 7C).

Hypoptopoma machadoi is distinguished from H. gulare by its deeper caudal peduncle (caudal-peduncle depth 9.0–12.0 (10.2) vs. 7.2–9.1 (8.7); t_(16.298), p < 0.001); by its greater number of premaxillary (16–25 (20) vs. 12–16 (14); t_(16.298), p < 0.001) and dentary teeth (14–21 (17) vs. 10–14 (12); t_(12,068), p < 0.001); by having lanceolate plates at caudal-fin base with light brown spot, symmetrically shaped, shortly extended over branched rays; spot followed by three vertical bands variably defined, with anterior band not continuous along midline with the basal spot (vs. lanceolate plates at caudal-fin base with dark spot, asymmetrically shaped, slightly more extended over lower-lobe branched rays; this spot is followed by two V-shaped bars, anterior bar variably developed on the upper lobe but always connected with basal spot) (fig. 17B); and by having the dorsal fin with typically three bars, without triangular spot at base (vs. dorsal fin with roughly triangular dark brown spot extended over base of anterior 3–4 branched rays, followed typically by 3–4 bars) (fig. 17G).

Hypoptopoma machadoi is distinguished from H. steindachneri by having a single paranasal plate (vs. presence of two or more paranasal plates) (fig. 7B–C), second infraorbital in contact with nasal and pararostral plates (vs. second infraorbital entirely separated from nasal and pararostral plates), and ventral canal-bearing plate undivided (vs. canal-bearing plate typically subdivided) (fig. 5A–B).

Description

Morphometric and meristic data presented in table 17. Body robust; greatest body depth at dorsal-fin origin. Dorsal profile of head and body straight from tip of snout to dorsal-fin origin, slightly angled dorsally at posterior tip of supraoccipital; straight from dorsal-fin origin to anteriormost procurrent caudal-fin ray. Head moderately depressed, almost as wide as cleithral width; lateral process of lateral ethmoid bone visible dorsally. Snout rounded in dorsal view; dorsally, slightly concave anterior to naris. Posterior surface of bony pit of nasal organ sharply inclined. Trunk cross section between pectoral-fin and pelvic-fin origins slightly triangular, ovoid to progressively rounded posterior to dorsal fin, progressively compressed posterior to adipose-fin base.

Eyes relatively large, positioned closer to posterior tip of compound pterotic than to tip of snout. Ventral margin of orbit located on ventral surface of head. Dorsal interorbital distance/ventral interorbital distance ratio changing from <1 to >1 during ontogeny.

Total plates in lateral medial series typically 21–22 (22). Dorsal series plates 18–19 (19); middorsal series plates 3–4 (4); midventral series plates 12–13 (13), three plates anterior to first ventral series plate; ventral series plates 18–19 (19). Second plate of midventral series contacting two plates of medial series.

Abdomen covered by paired series of lateral sickle-shaped plates, with unequal number of plates between left and right series, 3–10 each; anterior azygous plate usually present; medial series of plates, if present (47% of 316 individuals examined), not forming well-defined series. Single anal plate present. Thoracic plates present, 2–6. Preopercular canal present, semicircular; anteriormost pore located between ventral canal-bearing plate and fourth infraorbital; posterolateral margin of canal-bearing plate and lateral margin of fourth infraorbital variably developed, framed by notch at posterolateral margin of canal-bearing plate and ventral margin of fourth infraorbital.

Small odontodes evenly distributed on head. Odontodes along rostral margin of snout not arranged in well-defined series, without odontode-free discontinuity between ventrad and dorsad odontodes. Odontodes dorsal to tip of snout small, slightly larger than those on dorsal surface of head. Lamina of trunk plates with odontodes arranged in longitudinal rows, becoming progressively smoother ontogenetically; marginal odontodes present in mature adults.

Total vertebrae 26. Premaxillary teeth 16–25 (20); dentary teeth 14–21 (17). Maxillary barbels short; in adults, slightly surpassing anterior margin of ventral canal-bearing plate.

Dorsal-fin origin located slightly posterior to vertical through pelvic-fin origin. Depressed dorsal fin reaching to vertical through distal half of anal-fin base. Pectoral fin reaching to vertical through midpoint between anus and anal-fin origin. Pectoral spine with serrae along posterior margin, individual serrae oriented orthogonal to spine shaft. Extension of serrae along pectoral spine margin reduced ontogenetically from proximal two-thirds in smaller specimens to middle third in larger specimens. Depressed pelvic fin not reaching to anal-fin origin; unbranched and first branched rays of equal length. Caudal-fin margin concave; upper and lower lobes equal. Adipose fin present.

Color in alcohol

Ground color tan and light brown. Melanophores light to dark brown, clustered on trunk and at base of plates, yielding mottled appearance. Pigmentation slightly more concentrated dorsally on head, along narrow area betweeen compound pterotic, cleithral process and opercle, at base of dorsal and pectoral fins, and on anterior surface of lip. Deep-lying melanophores arranged as series of blotches posterior to dorsal-fin base. Midlateral stripe mostly along trunk medial series of plates. Ventral surface of body mostly unpigmented except for scattered melanophores on posterior portion of trunk, anterolateral margin of cleithra and posterior tip of cleithral process, lateral border of canal-bearing plates, and lateral portions of lateral abdominal series. Paired dorsal and anal fins with dark brown bars, aligned roughly orthogonal to the rays. Basal dark spot on anterior dorsal-fin branched rays typically not developed; if present, spot poorly defined. Lanceolate plates at base of caudal fin with light brown spot, symmetrically shaped and shortly extended over branched rays, followed by typically three vertical bands variably defined, with anterior one not continuous in the middle with basal spot; tips of lobes variably pigmented (fig. 17G).

Sexual dimorphism

Males with genital papilla small, not clearly separated from tubelike anal papilla. Males without patch (or patch poorly developed) of tightly arranged small odontodes oriented as a swirl on plates lateral to anal region. Female anus tubular, without separate urogenital papilla. In females, size and arrangement of odontodes on plates lateral to anus similar to adjacent plates, without distinct patch of differentially arranged odontodes.

Distribution

Known for the Rio Orinoco basin in Venezuela, including the Rio Meta drainage in Colombia (fig. 39).

Remarks

Specimens collected in the Río Meta drainage and in localities along the southern tributaries of the Río Orinoco are slightly more slender and with fewer caudal-fin bars than specimens that originated in localities from northern tributaries to the Río Orinoco.

Etymology

The specific epithet machadoi is a patronymic honoring Antonio Machado-Allison, in recognition of his lifelong dedication and contributions to Neotropical ichthyology.