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10 March 2017 Description of a New Blind and Rare Species of Xyliphius (Siluriformes: Aspredinidae) from the Amazon Basin Using High-Resolution Computed Tomography
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Abstract

Xyliphius sofiae, new species, is described based on a unique specimen exhibiting four autapomorphies: eyes absent vs. present (though reduced); color pale, lacking pigment vs. head and body darkly pigmented; branchiostegal rays five vs. four; and unculiferous tubercles on posterior body distributed evenly vs. enlarged unculiferous tubercles typically arranged in five distinct rows above pelvic-fin base to posterior end of caudal peduncle. In addition, the pectoral fin of X. sofiae, new species, has one ossified proximal radial vs. two in congeners (except X. magdalenae, not examined). Xyliphius sofiae, new species, differs from all congeners except X. lepturus by snout tip elongated and narrowly rounded vs. short and broadly rounded, often with small median notch; fifth ceratobranchial relatively narrow with elongate acicular teeth vs. broadly expanded, leaf-shaped, with shorter and broader, conical teeth; anterior limits of branchial apertures separated by distance less than length of aperture vs. greater than length of aperture; anal-fin rays modally nine vs. seven; and lateral line extending onto base of caudal-fin rays vs. finishing in hypural region. Based on the single specimen collected in the main channel of the Río Amazonas near Iquitos, Peru, we describe the osteology of X. sofiae, new species, using a non-invasive technique: high-resolution X-ray computed tomography (HRXCT). We consider Xyliphius lombarderoi Risso and Risso, 1964, a species based on a unique holotype that is now lost, to be a subjective junior synonym of X. barbatus Alonso de Arámburu and Arámburu, 1962. Variable characteristics are summarized for the seven species of Xyliphius treated here as valid, and their distributions are plotted based on a comprehensive review of museum specimens.

XYLIPHIUS Eigenmann, 1912 is one of 13 genera of Aspredinidae, a family with about 43 valid species commonly known as banjo catfishes (Friel, 2003; Carvalho et al., 2015; Friel and Carvalho, 2016). Including the new taxon described here, Xyliphius contains seven valid species distributed in major watersheds throughout South America, such as the Magdalena, Maracaibo, Orinoco, Amazon, Paraná-Paraguay, and Tocantins (Friel, 2003; Figueiredo and Britto, 2010). In the Western Amazon and Orinoco basins, two species occur together in large tributaries on the Andean piedmont: Xyliphius lepturus Orcés, 1962 and Xyliphius melanopterus Orcés, 1962. Xyliphius anachoretes Figueiredo and Britto, 2010 is known from only two specimens from the upper reaches of the Tocantins basin on the Brazilian Shield and is highly disjunct from congeners. Xyliphius magdalenae Eigenman, 1912 and X. kryptos Taphhorn and Lilyestrom, 1983 occur west of the Andes as endemics to the Magdalena and Maracaibo basins, respectively. Calviño and Castello (2008) reported on specimens of Xyliphius barbatus Alonso de Arámburu and Arámburu, 1962 trawled from depths of 35–45 m in the Middle Paraná River. Specimens of Xyliphius are rare in museum collections due to their occurrence in the main channels of medium to large rivers and habitats that require special techniques (e.g., trawling) or conditions (dry downs during dam construction) for effective sampling.

According to Friel (1994), the monophyly of Xyliphius is supported by eight unambiguous character state changes: cranium lacking orbital concavity; pterotic laminar process directed laterally and rounded; premaxilla displaced laterally; suprapreopercle present; lateral end of posterior ceratohyal expanded; bipartite nasal; papillae present on lower jaw; and skin with flattened unculiferous tubercles. Other characteristics not unique to Xyliphius but useful for identification include: anterior margin of fleshy tube enclosing anterior nares with finger-like papillae; coronomeckelian bone absent; Meckel's cartilage with high ascending process; and anterior margin of pectoral-fin spine smooth, without serrations (Friel, 1994).

We describe a new species of Xyliphius based on a single specimen from the Amazon River channel near Iquitos, Peru. Osteological descriptions are based on high-resolution X-ray computed tomography (HRXCT), a non-invasive technique that reconstructs a virtual skeleton in digital form. High-resolution X-ray computed tomography has been recently used to recover osteological data for species rare in museum collections (Schaefer, 2003; Schaefer and Fernández, 2009; Carvalho and Albert, 2011; Lundberg et al., 2014).

MATERIALS AND METHODS

Measurements were taken point to point with a digital caliper and are expressed as percent of the standard length (SL), except subunits of head, expressed as percent of the head length (HL). Measurements follow Friel (1995) and Cardoso (2010), except for posterior cleithral-process length and head length. Posterior cleithral-process length was taken from the anterior lateral margin of the cleithrum to the posterior tip of process. Head length was taken from snout tip to point along posterior margin of supraoccipital, aside base of supraoccipital process (process visualized beneath thick skin by adpressing caliper tip).

The holotype was scanned at the High-Resolution X-ray Computed Tomography Facility, The University of Texas, Austin, using an NSI scanner with the following settings: high power, 150 kV FeinFocus X-ray source, 0.17 mA, no filter, Perkin Elmer detector, 0.25 pF gain, 2 fps (499.893 ms integration time), no binning, no flip, source to object 133.811 mm, source to detector 1316.553 mm, continuous CT scan, no frames averaged, 0 skip frames, 3000 projections, 7 gain calibrations, 0.762 mm calibration phantom, data range [–50, 600] (grayscale range adjusted from NSI defaults). Voxel size 0.00946 mm. Total slices 1820.

The scan was taken along the long axis of the specimen from snout tip to about the sixth vertebrae. Visualizations and sectioning of the 3D models were produced as 8-bit jpeg files in the software package VGStudio MAX® V1.2.1, at The Academy of Natural Sciences of Drexel University (ANSP). The renderings appear similar to photographs and represent differences in X-ray attenuation based on thickness and density of anatomical structures. The shadowing option in VGStudio was used to enhance 3D visualization. Figures were captured as still frames from HRXCT digital animations and edited for publication in Adobe Photoshop®CS. Cut through videos along the axial, sagittal, and frontal planes and raw images (8-bit jpeg) of X-ray slices were uploaded to Morphobank ( www.morphobank.org, project number 2361).

Vertebral counts and descriptions of the caudal region are based on digital radiographs captured at ANSP with a Kevex MicroFocus X-Ray Source and Varian PaxScan image receptor. Vertebral counts include five vertebrae modified into the Weberian apparatus, and the PU1+U1 and U2 elements of the caudal skeleton are counted as a single vertebra. Comparative material was cleared and stained (CS) according to Taylor and Van Dyke (1985). Using Adobe Illustrator®CS and Adobe Photoshop®CS, illustrations were traced and stippled from digital images taken with a Nikon D90 of cleared and stained specimens in 95% glycerin. Whole specimens were digitally imaged with a Nikon D90 using the photo-tank technique described by Sabaj Pérez (2009).

Anatomical descriptions focused on characteristics described in previous phylogenetic studies of the family Aspredinidae (Friel, 1994; de Pinna, 1996; Cardoso, 2008). Anatomical terminology generally follows the Teleost Anatomical Ontology (TAO; Dahdul et al., 2010), an integral part of the Uberon Ontology covering anatomical structures in animals (Mungall et al., 2012;  http://uberon.github.io/). GenSeq nomenclature follows Chakrabarty et al. (2013). Genomic DNA was extracted using a DNeasy tissue extraction kit (Qiagen) on muscle and/or fin clips fixed in 96% ethanol and stored at –80°C. Sequences of mitochondrial encoding cytochrome oxidase subunit I (COI) and nuclear encoding myosin, heavy polypeptide 6 (Myh6) and SH3 +PX domain-containing 3-like protein (SH3PX3) were amplified following Herbert et al. (2003) and Li et al. (2007), respectively, and sequenced at Functional Biosciences (Madison, WI). Institutional abbreviations follow Sabaj Pérez (2014).

Xyliphius sofiae Sabaj, Carvalho, and Reis, new species

urn:lsid:zoobank.org:act:AD6D52EE-CF9D-48CA-83FD-4F0C90868920

Figure 1, Tables 1, 2

Xyliphius sp.—Arce et al., 2013:572 [phylogeny outgroup, listed as likely undescribed species].

Fig. 1. 

Holotype of Xyliphius sofiae, ANSP 182322, 44.1 mm SL, Río Amazonas in vicinity of Iquitos, Loreto, Peru. (A–C) Alcohol preserved (scale bar = 5 mm). (D) Live. Photos by M. Sabaj.

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Table 1. 

Morphometric data for holotype of Xyliphius sofiae.

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Table 2. 

Summary of characteristics variable within valid species of Xyliphius based on literature and examined material (Alonso de Arámburu and Arámburu, 1962; Taphorn and Lilyestrom, 1983; Calviño and Castello, 2008; Figueiredo and Britto, 2010). HL = head length, SL = standard length.

i0045-8511-105-1-14-t02.eps

Holotype.—ANSP 182322, 44.1 mm SL (right pelvic fin taken for tissue), Peru, Loreto, Maynas, Río Amazonas, main channel in vicinity of Iquitos, 03°43′21″S, 073°12′14″W, M. Sabaj, M. Arce, A. Bullard, O. Castillo, C. DoNascimiento, et al., 13 August 2005. GenBank accession numbers (GenSeq-1): KC555831 (rag1; Arce et al., 2013), KC555965 (16S; Arce et al., 2013), KU736764 (COI; this study), KU736765 (Myh6; this study), KU736766 (SH3PX3; this study).

Diagnosis.—Xyliphius sofiae is distinguished from congeners by four autapomorphies: eyes absent vs. present (though reduced); color pale, lacking pigment (Fig. 1) vs. head and body darkly pigmented (Fig. 2); branchiostegal rays five vs. four; unculiferous tubercles on posterior body distributed evenly vs. enlarged unculiferous tubercles typically arranged in five distinct rows from above pelvic-fin base to posterior end of caudal peduncle. In addition, the pectoral fin of X. sofiae has one ossified proximal radial vs. two in congeners (except X. magdalenae, not examined). Xyliphius sofiae is distinguished from all congeners except X. lepturus by having the snout tip elongated and narrowly rounded (Fig. 3A, C) vs. short and broadly rounded, often with small median notch (Fig. 3B, D); fifth ceratobranchial relatively narrow with two or three irregular rows of acicular teeth vs. broadly expanded with larger conical teeth; anterior limits of the branchial apertures separated by a distance smaller than length of aperture vs. greater than length of aperture; anal-fin rays modally nine vs. seven; and lateral line extending onto base of caudal-fin rays vs. finishing in hypural region.

Fig. 2. 

Lateral view of select species of Xyliphius. (A) X. barbatus, MLP 6798, holotype, 92.0 mm SL. (B) X. lepturus, ANSP 128941, 94.5 mm SL. (C) X. magdalenae, CZUT-IC 1288, 75 mm SL. (D) X. melanopterus, FMNH 99495, 120.4 mm SL. (E) X. kryptos, MCNG 27310, 112.0 mm SL. Photos by M. Sabaj (A), T. Carvalho (B, E), J. Garcia-Melo (C), and A. Thomaz (D).

i0045-8511-105-1-14-f02.tif

Fig. 3. 

Ventral view of head. (A) Xyliphius sofiae, ANSP 182322, holotype, 44.1 mm SL. (B) X. melanopterus, FMNH 99495, 120.4 mm SL. (C) X. lepturus, ANSP 128941, 94.5 mm SL. (D) X. barbatus, MLP 6798, 92.0 mm SL. Photos by M. Sabaj.

i0045-8511-105-1-14-f03.tif

Description.—Morphometric data summarized in Table 1. Head and body depressed. Dorsal profile rising gently from snout tip to dorsal-fin origin with shallow convexity between anterior nares and occipital region; then straight, descending gradually to end of caudal peduncle. Ventral profile more or less flat except for abrupt rise from mouth gape to snout tip. Rostrum bluntly triangular in dorsal view, lacking medial notch. Caudal peduncle long and slender, rounded in cross section.

Eyes absent. Anterior nares located dorsally about midway between snout tip and posterior rictus of mouth, enclosed by fleshy tube with posterior portion enlarged, flap-like; anterior margin of tube with two finger-like papillae projected posteriorly. Posterior nares lacking fleshy tube, aligned with posterior insertion of maxillary barbel. Rostrum overhanging inferior mouth; gape large, spanning distance between lateral contours of snout. Upper lip rugose with small flattened tubercles; lower lip with 31 elongate papillae, all unbranched; length of longest papilla about ten times its width (Fig. 3A).

Three pairs of barbels, all simple. Maxillary barbel long, reaching vertical through base of first branched dorsal-fin ray; leading edge scalloped with low, ridge-like tubercles. Mental barbels staggered, surfaces slightly rugose. Outer mental barbel long, surpassing posterior margin of scapulocoracoid bridge, and nearly twice as long as inner mental barbel. Opercular opening entirely ventral, concealed by large rounded membranous flap, and nearly reaching its counterpart anteriorly (i.e., anterior limits of opercular openings separated by distance less than length of aperture).

Skin roughened with flattened unculiferous tubercles. Largest tubercles appear as small irregular plates tightly spaced on skin covering neurocranium. Smaller, subtriangular, weakly imbricate tubercles on posterior flanks and not arranged in distinct rows. Smallest tubercles on ventral surfaces. Enlarged and slightly raised tubercles on underside of overhanging snout. Small, oblique, slit-like pore at axilla of pectoral fin. Base of caudal fin covered with skin bearing small triangular tubercles.

Based on HRXCT data, external surfaces of skull-roof bones with pitted texture, lacking bony knobs. Mesethmoid long and deep with cornua weakly projected laterally, elongate anterolateral concavity for articulation with premaxilla (completed by lateral process from ventral face), slight superficial posterolateral expansion for suture with lateral ethmoid, and elongate posterior rami enclosing nearly one-third of anterior cranial fontanel (Figs. 4, 5). Anterior face of mesethmoid with small bony tubercles directed anteroventrally; anterior margin separated by distinct anteromedial notch continuing as dorsal median furrow to midlength (notch not visible in whole specimen). Posterior portion of mesethmoid not elevated, level with anterior portion of frontals. Lateral ethmoid with large internal chamber housing olfactory bulb and large circular foramen on anterolateral face for connection between olfactory bulb and olfactory organ (Fig. 6C, E, F). Lateral ethmoid extended dorsoposteriorly, contributing to small portion of dorsal surface and lateral margin of neurocranium, partially enclosing anterolateral margin of frontal. Lateral ethmoid with large protruding lateral process articulating with central mesial face of autopalatine (Figs. 4A, 5A). Frontal moderately compact with deeply pitted surface; length about three times width; lateral margin lacking orbital concavity; contacting supraoccipital via posteriorly directed arms. Anterior cranial fontanel elongated and narrow, length about 7.5 times width; anterior third enclosed by mesethmoid, remainder by frontals. Posterior cranial fontanel similarly long and narrow, length over nine times width; enclosed mostly by frontals except posteriormost rim formed by supraoccipital. Epiphyseal bar centered along cranial fontanel with broad median suture over one-fifth as long as distance between anterior and posterior limits of fontanel. Supraoccipital compact, greatest length about 1.5 times greatest width; surface smooth anteriorly, pitted posteriorly; posterior process narrow, length nearly three times width, contacting dorsal keel of Weberian complex vertebrae. Sphenotic curved, contacting pterotic, supraoccipital, and posterior half of lateral margin of frontal; surface pitted. Pterotic expanded anteriorly as shelf contacting posterolateral portion of sphenotic; anterolateral margin concave in dorsal view; surface pitted. Pterotic expanded by lateral blade that is somewhat rounded in dorsal view. Supratemporal fossa distinct, enclosed by posterior portions of pterotic and supraoccipital at their suture. Epioccipital compact, contacting supraoccipital anteriorly, pterotic laterally, and posttemporal-supracleithrum posteriorly; dorsal face contributing to skull roof and posteromedial face contributing to posterior wall of cranium. Posttemporal-supracleithrum plate-like with pitted surface, contributing to dorsal aspect of skull; anterolateral process overlying dorsal process of cleithrum.

Fig. 4. 

HRXCT model of skull and anterior body of Xyliphius sofiae, ANSP 182322, holotype, 44.1 mm SL. (A) Dorsal view. (B) Lateral view of left side.

ang: anguloarticular; at: antorbital tubule; br: branchiostegal rays; cl: cleithrum; co: scapulocoracoid; cv: complex vertebrae; den: dentary; en: endopterygoid; epo: epioccipital; ex: extrascapular; fr: frontal; hyo: hyomandibula; ih: interhyal; io1: infraorbital 1; iop: interopercle; iot: infraorbital tubules; lal: lateral line tubules; let: lateral ethmoid; mc: mandibular canal tubules; mes: mesethmoid; met: metapterygoid; mnp: middle nuchal plate; mx: maxilla; na: nasal; op: opercle; pal: autopalatine; pch: posterior ceratohyal; pfr: pectoral-fin rays; pmx: premaxilla; po: preopercle; ps: pectoral-fin spine; pto: pterotic; pv5: parapophysis of vertebra five; qu: quadrate; rad: pectoral-fin radial; rb6: rib six; ret: retroarticular; sc: posttemporal-supracleithrum; soc: supraoccipital; spo: sphenotic; sup: suprapreopercle; v6: vertebrae six. Scale bar = 2 mm.

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Fig. 5. 

HRXCT model of skull and anterior body of Xyliphius sofiae, ANSP 182322, holotype, 44.1 mm SL. (A) Ventral view. (B) Mesial view of left side. ach: anterior ceratohyal; bb: basibranchials; bo: basioccipital; br: branchiostegal rays; cl: cleithrum; co: scapulocoracoid; cv: complex vertebrae; den: dentary; epo: epioccipital; exo: exoccipital; fr: frontal; let: lateral ethmoid; mc: mandibular canal tubules; mes: mesethmoid; mnp: middle nuchal plate; mx: maxilla; orb: orbitosphenoid; pal: autopalatine; pas: parasphenoid; pch: posterior ceratohyal; pfr: pectoral-fin rays; pmx: premaxilla; pro: prootic; ps: pectoral-fin spine; pte: pterosphenoid; pto: pterotic; rad: pectoral-fin radial; ret: retroarticular; sc: posttemporal-supracleithrum; soc: supraoccipital; spo: sphenotic; tr: tripus; uh: urohyal; v5: vertebrae five; vh: ventral hypohyal. Scale bar = 2 mm.

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Fig. 6. 

HRXCT model of select bones in Xyliphius sofiae, ANSP 182322, holotype, 44.1 mm SL. Bones associated with the anterior cephalic canals of the lateral line system (anterior is left) in dorsal (A) and lateral (B) views. Entire lateral ethmoid (anterior is left) in ventral (C) and frontal (D) view. (E) Partial lateral ethmoid in dorsal view cut to about half of its depth (anterior is left). (F) Partial lateral ethmoid in frontal view cut to about vertical through origin of lateral process. at: antorbital tubule; i1–i6: infraorbital branches one to six; io1: infraorbital one; iot: infraorbital tubules; lp: lateral process of lateral ethmoid; na: nasal; obc: olfactory bulb chamber; s1–s3: supraorbital branches one to three. Scale bar = 2 mm.

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Premaxilla broad and plate-like with anterior and posterior margins somewhat rounded, surface rugose; teeth absent. Premaxilla lateroventral to mesethmoid and remote from counterpart; dorsolateral margin contacting anterior wing of infraorbital 1. Maxilla long and slender, distally bifurcate for about two-thirds its length with ventrolateral arm longer than dorsomedial one. Dentary slender with symphyseal gap, forming broad arc to accommodate large gape (Fig. 5A). Dentary teeth conical, curved slightly inwards; arranged in two rows, outer row occupying symphyseal half of dentary length, inner row more restricted to symphyseal portion of bone (Fig. 7A). Coronomeckelian bone absent.

Fig. 7. 

HRXCT model of suspensorium plus lower jaw (A) and hyoid arch (B–C) of Xyliphius sofiae, ANSP 182322, 44.1 mm SL. ach: anterior ceratohyal; ang: anguloarticular; br: branchiostegal rays; den: dentary; en: endopterygoid; hyo: hyomandibula; ih: interhyal; iop: interopercle; mc: mandibular canal tubules; met: metapterygoid; op: opercle; pch: posterior ceratohyal; pop: preopercle; qu: quadrate; ret: retroarticular; sup: suprapreopercle; uh: urohyal; vh: ventral hypohyal. Scale bar = 2 mm.

i0045-8511-105-1-14-f07.tif

Hyomandibula with anterodorsal process contacting ventral face of sphenotic, concave anteroventral face contacting quadrate, and laterally associated with preopercle. Quadrate subtriangular, anterior condyle articulating with retroarticular and anguloarticular, not contacting ventral margin of small metapterygoid (except perhaps by cartilage). Endopterygoid squarish, located beneath and medial to posterior end of autopalatine. Autopalatine moderately compact, length about six times minimum diameter, posterior end truncate, not bifurcate. Opercle boomerang-shaped with posterior wing about twice as long as ventral one. Interopercle present, wedge shaped with dorsoposterior margin firmly attached to ventral wing of opercle (Fig. 7A).

Urohyal present, rounded anteriorly with three posteriorly directed wings and distinct foramen in central portion visible in dorsal view (Fig. 7C). Two ossified basibranchials. First hypobranchial ossified. Dorsal hypohyal absent. Ventral hypohyal triangular. Anterior ceratohyal broad with expanded lamina along anterolateral margin, contacting posterior ceratohyal via interdigitated suture. Interhyal present, compact, squarish, located anterodorsal to posterior portion of posterior ceratohyal. Branchiostegal rays five; outermost (fifth) with anterior half expanded, approximating size of posterior ceratohyal; fourth branchiostegal ray also with expanded basal portion; remaining branchiostegals 3–5 becoming gradually shorter and more slender, ray-like. Five ceratobranchials, all bearing short gill rakers; fifth ceratobranchial with two or three irregular rows of acicular teeth along dorsal surface of anterior half (Fig. 8B). Four epibranchials, third bearing distinct uncinate process (Fig. 8). First and second pharyngobranchials absent or unossified; third and fourth ossified, suspending expanded tooth plate with elongate acicular teeth.

Fig. 8. 

HRXCT model of branchial arches (A–B, left side, dorsal view, anterior up), and 5th ceratobranchial of cleared and stained specimens (left side, dorsal view, anterior up). (A) Xyliphius sofiae, ANSP 182322, holotype, 44.1 mm SL (scale bar = 2 mm). (B) Unobscured dorsal view of 5th ceratobranchial in ANSP 182322 (scale bar = 1 mm). (C) Xyliphius lepturus, FMNH 99488, 72.1 mm SL (scale bar = 1 mm). (D) Xyliphius melanopterus, FMNH 99493, 81.9 mm SL (scale bar = 1 mm). bb: basibranchial; cb: ceratobranchial; cb5: ceratobranchial five; eb: epibranchial; hb: hypobranchial; pb: pharyngobranchial; tp: tooth patch.

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Nasal composed of two separate tubular ossifications between supraorbital sensory pores 1–2 and 2–3, respectively (Fig. 6A). Infraorbital 1 with anterior half curved medially, finishing dorsal to premaxilla (Fig. 4A); mesial limb short; lateral face notched with foramen for canal passage posteriorly (Fig. 6A, D). Remaining infraorbitals reduced to series of small, disjointed tubules, some with small ventrolateral ossification associated with branch for infraorbital canal pores i4–i6. Additional small canal-like ossifications situated between pores i1–i2, ventrolateral to infraorbital sensory branch 2, and dorsomedial to infraorbital 1. Infraorbital canal (Fig. 6A) begins with pore (i1) and enters foramen at midpoint of dorsal margin of infraorbital 1; second pore (i2) at end of branch posteromedial to pore 1. Infraorbital canal exits through foramen in posterior notch in infraorbital 1 and begets four branches ending in pores i3–i6. Preopercle-mandibular canal (Fig. 7) incomplete anteriorly with one short tubular ossification ventral to posterior portion of dentary, separated by gap from second similar ossification beneath posterior portion of retroarticular. Second ossification separated by gap from disjointed series of closely set ossified tubules finishing with canal passage into preopercle. Preopercle-mandibular canal associated with hyomandibula posteriorly. Suprapreopercle present, small, bearing canal, received by notch in hyomandibula anteriorly and contacting pterotic posteriorly. Extrascapula present, small tubular ossification located between pterotic and posttemporal-supracleithum (Fig. 4A, B) and at ramification of postotic sensory branch 2. Lateral line complete, not associated with fourth parapophysis, exiting posterolateral corner of posttemporal-supracleithum and extending onto base of caudal-fin rays as simple ossified tubes.

Dorsal keel of Weberian complex with straight margin reaching surface of body. Parapophysis of fourth vertebra forming broad lamina partially encapsulating gas bladder (Fig. 9C). Posterior margin of parapophysis of fourth vertebra in complete contact with ventrally displaced parapophysis of fifth vertebrae. Parapophysis of fifth vertebra long, extending to body wall and beyond lateral limits of parapophysis of fourth vertebra. Distal margin of fifth parapophysis obliquely truncate, not distinctly expanded. No evidence of separate anterior nuchal plate. Middle nuchal plate small, posterolaterally contacting posterior nuchal plate, distant from dorsal keel of Weberian complex. Posterior nuchal plate with acute triangular wing directed anterolaterally (visible in whole specimen). Total vertebrae 36. Vertebrae 7–27 bearing horizontal transverse processes. Hemal and neural spines moderately elongate, those on posterior portion of caudal peduncle obliquely orientated. Seven pairs of ribs on vertebrae 6–12.

Fig. 9. 

Ventral view of Weberian complex in select species of Xyliphius (anterior is top). (A) X. lepturus, FMNH 99488, 72.1 mm SL. (B) X. melanopterus, FMNH 99493, 81.9 mm SL. (C) Xyliphius sofiae, ANSP 182322, 44.1 mm SL. cv: complex vertebra; gbc: gas bladder chamber (line points to portion encapsulated by bone in B); hc: hemal canal; in: intercalarium; lal: lateral line tubules; pcv: parapophysis complex vertebra; pv5: parapophysis vertebra five; r6: rib 6; sc: scaphium; tr: tripus; v6: vertebra six. Scale bar = 2 mm.

i0045-8511-105-1-14-f09.tif

Dorsal fin I,4. First ray simple, slender, stiffened (not pungent), and elongated distally as flexible filament; anterior face lacking serrations, but rugose with small plate-like tubercles resembling those on body. Soft rays