Description of a New Genus and Two New Species of Indo-Pacific Clingfishes (Gobiesocidae: Diademichthyinae) with Redescription and Reassignment of Two Species Previously Assigned to Lepadichthys Waite, 1904

A new genus and two new species of Indo-Pacific clingfishes are described in this study. The new genus, Flabellicauda, belongs to the Diademichthyinae and can be distinguished from other genera currently placed in this subfamily by the following combination of characters: snout moderate in length and slightly pointed, not extremely long or strongly rounded; oral cleft very small, restricted to anterior tip of snout, posterior portion of both jaws covered by thick skin of snout; gill opening a tiny, narrow slit, dorsalmost point level with base of 9th to 14th (usually 12th, rarely 9th) pectoral-fin ray in lateral view; gill membrane attached to isthmus; two rows of gill filaments on gill arches 1–3; extremely small “single” adhesive disc, its length 8.1–13.5% SL; center of disc flat, without cavity; disc papillae flattened, similar in size across disc surface; preopercular lateral-line canal and associated pores absent; dorsal, anal, and caudal fins connected via thin membrane, giving appearance of single, continuous median fin around posterior part of body; and upper and lower hypural plates completely fused, forming large fan-like hypural complex. Two new species are described and assigned to Flabellicauda, new genus, including F. alleni, new species (type species of Flabellicauda, new genus), and F. cometes, new species. Two additional species previously assigned to Lepadichthys are transferred to Flabellicauda, new genus, including F. bolini, new combination, and F. akiko, new combination. Among species of Flabellicauda, new genus, F. akiko is unique in having the following characters: head sensory canal pores poorly developed, including 1 nasal and 1 postorbital pore (vs. usually 2 nasal, 2 lacrimal, and 2 postorbital pores in F. alleni, new species, and F. bolini; 2 nasal pores in F. cometes, new species); upper end of gill opening level with base of 9th or 10th pectoral-fin ray in lateral view (vs. 12th to 14th); disc region A with papillae at center (vs. disc region A without papillae at center); and body background color red in life, with white stripes along body (vs. body background color black or maroon in life, with white stripes along body). Although F. alleni, new species, is very similar to F. bolini, the former differs from the latter in having a higher number of gill rakers (viz., 5–8 [modally 6, rarely 5], 6–8 [6], and 6–8 [7] on the first, second, and third gill arch, respectively, and 18–24 [19] total gill rakers [first + second + third arch] in F. alleni, new species, vs. 4–6 [5] on the first, second, and third arch, respectively, and 12–17 [14] total gill rakers in F. bolini). In addition to the meristic difference, head length, pre-disc length, orbit diameter, and caudal-peduncle length and width proportions further aid to distinguish F. alleni, new species, from F. bolini. Examined specimens of F. alleni, new species, were collected from Sri Lanka and southeast Asia, whereas those of F. bolini were collected from Papua New Guinea, Vanuatu, and Fiji; the range of the two species are not known to overlap. Flabellicauda cometes, new species, can be easily distinguished from F. alleni, new species, and F. bolini in having the following characters: 10–12 dorsal-fin rays (vs. 12–15 [13]); 9–11 anal-fin rays (vs. 10–13 [11], rarely 10); head sensory canal pores poorly developed, including 2 nasal and 1 postorbital pores. Notes on the ecology of each of the four species of Flabellicauda, new genus, are also provided.

T HE family Diademichthyidae was introduced by Whitley (1950) for the distinctive Urchin Clingfish Diademichthys lineatus. Briggs (1955) redefined it as a subfamily of the Gobiesocidae and included both Diademichthys and Lepadichthys. Later, Briggs (1976) and Fricke (2014) added Discotrema and Unguitrema, respectively, to the Diademichthyinae. In their phylogenetic investigation of the Gobiesocidae, Conway et al. (2020) recovered the Diademichthyinae as a polyphyletic group and, in order to achieve monophyly, recommended that it be expanded to include several additional genera formerly included in the Aspasminae, Diplocrepinae, and Protogobiesocinae by Briggs (1955) and Fricke et al. (2016). Following Conway et al. (2020), the total number of genera included in the Diademichthyinae is 15, which can be artificially separated into two groups based on whether they exhibit a ''single'' or ''double'' adhesive disc (see Briggs, 1955: fig. 1), a character that has traditionally been reserved for the diagnosis of subfamilylevel taxa (Briggs, 1955).
The genus Lepadichthys was established by Waite (1904) for Lepadichthys frenatus, based on specimens collected at Lord Howe Island, Tasman sea, Australia. Later Regan (1921), added L. coccinotaenia, described based on specimens collected from the southwestern Indian Ocean (along the coast of South Africa), and Whitley (1943) added L. sandaracatus, described based on specimens collected from the southeastern Indian Ocean (along the coast of Western Australia). In his review of gobiesocid fishes, Briggs (1955) placed Lepadichthys within his Diademichthyinae, provided a rediagnosis for the genus, and also described L. minor, based on specimens collected from the Sulawesi Sea (western Pacific). Subsequent to Briggs's (1955) revision, ten species of Lepadichthys have been described from throughout the Indo-Pacific, including (in order of year of description): L. bolini, L. ctenion, L. erythraeus, L. lineatus, L. caritus, L. springeri, L. akiko, L. bilineatus, L. trishula, and L. conwayi (Briggs, 1962(Briggs, , 1966(Briggs, , 1969a(Briggs, , 2001Briggs and Link, 1963;Allen and Erdmann, 2012;Craig et al., 2015;Fujiwara et al., 2020;Fujiwara and Motomura, 2020a). In the most recent taxonomic work on the genus, Fujiwara and Motomura (2019a) showed that Lepadichthys misakius, previously regarded as a junior synonym of L. frenatus, is a valid species, and Fujiwara and Motomura (2020a) showed that L. springeri is a synonym of L. misakius. Presently, the total number of valid species of Lepadichthys is 14 (Fricke et al., 2021). Though the number of species of Lepadichthys has increased markedly after Briggs (1955), the diagnosis of the genus has never been revised. Hence, some species currently included in Lepadichthys do not match the current generic diagnosis (see explanation in . The results of a recent molecular phylogenetic study on clingfishes (Conway et al., 2020) showed that Lepadichthys, as currently defined, is likely polyphyletic based on the phylogenetic placement of the four species included in that study (L. akiko, L. bolini, L. misakius, and L. trishula).
As part of an ongoing taxonomic study of Lepadichthys, we observed consistent morphological variation among samples of the geographically widespread L. bolini, a species described by Briggs (1962) based on a single individual from Vanuatu. Further investigation revealed this material to comprise not one but instead three species, two of which are currently undescribed. Like L. bolini and the closely related L. akiko, the two new species exhibit a striking pattern in life comprising a series of white stripes along the body that contrast with a darker background color of black or maroon. In addition to this striking live color pattern, all four species exhibit a distinctive arrangement of the caudalfin skeleton, in which the hypural complex is represented by a single, large fan-shaped element (vs. separated into an upper and lower hypural plate in the majority of other gobiesocids). These apomorphic characters, in combination with a number of others, suggest to us that these four species represent a putative monophyletic group, which, based on the results of recent molecular phylogenetic work, is not closely related to members of Lepadichthys (including the type species, L. frenatus; see discussion). In this study, we describe the new genus Flabellicauda to accommodate four distinctive members of the Diademichthyinae, describe two new species, and provide redescriptions of Flabellicauda akiko and Flabellicauda bolini, both new combinations.

MATERIALS AND METHODS
Counts and measurements follow  except for upper-jaw length, which is measured from the anterior point of the upper lip to the junction between the lateral part of the upper lip and the skin of the snout, which restricts the mouth opening laterally. Measurements were made to the nearest 0.01 mm, except for standard length (SL), which was measured to the nearest 0.1 mm. Institutional codes followed Sabaj (2020). Data obtained from holotypes are presented first within descriptions, followed by data obtained from other specimens in parentheses (if different). Adhesive disc terminology follows Briggs (1955: fig. 1), and cephalic sensory canal pore terminology follows Shiogaki and Dotsu (1983: fig. 1) and Conway et al. (2017a: fig. 1), except that we use the term otic canal instead of postorbital canal (though retain the abbreviations PO1 and PO2 for the pores associated with this canal). Features of both the adhesive disc and cephalic sensory canal pores were observed using versatile staining with Cyanine Blue (Saruwatari et al., 1997). Osteological terminology follows Springer and Fraser (1976) and Conway et al. (2019). Osteological features were assessed via radiographs for the majority of specimens, but select specimens were cleared and double stained (CS) for bone and cartilage investigation using the protocol of Taylor and Van Dyke (1985). Computed tomography (CT) scans of select specimens of F. akiko, F. alleni, new species, and F. cometes, new species, were also obtained at the Karel F. Liem Bioimaging Facility (Friday Harbor Laboratories, University of Washington) using a Bruker (Billerica, MA) SkyScan 1173 scanner with a 1 mm aluminum filter at 60 kV and 110 lA on a 2240 3 2240 pixel CCD at a resolution of 8.8 lm. Specimens were scanned simultaneously in a 50 ml plastic Falcon tube (Corning, NY), in which they were wrapped with cheesecloth moistened with ethanol (70%) to prevent movement during scanning. The resulting CT data were visualized, segmented, and rendered in Horos (https:// horosproject.org) and Amira (FEI). The distributional map was prepared using GMT 5.3.1, using data from GSHHG (Wessel and Smith, 1996). Diagnosis.-A genus of the Gobiesocidae distinguished from other gobiesocid genera, except for Diademichthys, Discotrema, Lepadichthys, Lepadicyathus, and Unguitrema, by having a ''single'' adhesive disc, two rows of gill filaments on gill arches 1-3 (3 gills sensu Briggs, 1955), and the gill membrane attached to the isthmus. The new genus is distinguished from Discotrema and Unguitrema by the following combination of characters: snout slightly pointed (vs. strongly rounded in Discotrema and Unguitrema; Fig. 1A, D); center of disc flat, without cavity (vs. deep cavity present: see Briggs, 1976: fig. 1); and disc papillae flattened, similar in size across disc surface (vs. disc papillae of variable size across surface of disc, largest papillae dome-like, or pyramidal: see Briggs, 1976: fig. 1;Fricke, 2014: fig. 1c). The new genus is distinguished from Diademichthys, Lepadichthys, and Lepadicyathus by the following unique combination of characters: snout moderate in length (vs. extremely long in Diademichthys; Fig. 1A, C); oral cleft very small, restricted to anterior tip of snout, posterior portion of both jaws covered by thick skin of snout (vs. moderate, not covered by skin of snout in Diademichthys and Lepadichthys; Fig. 1A-C); preopercular lateral-line canal and associated pores absent (vs. present in Diademichthys and Lepadichthys); gill opening a tiny, narrow slit, dorsalmost point level with base of 9 th to 14 th (usually 12 th , rarely 9 th ) pectoral-fin ray in lateral view (vs. moderate in Diademichthys [7 th to 9 th ] and Lepadichthys [3 rd to 9 th , rarely 10 th ]); disc extremely small, its length 8.1-13.5% SL (vs. moderate in Lepadichthys [13.9-20.8% SL] and Lepadicyathus [18.1-19.0% SL]); dorsal, anal, and caudal fins strongly connected with membrane, giving appearance of single, continuous median fin around posterior part of body (vs. completely separated in Diademichthys, connected by membrane but with distinct notch between fins in Lepadichthys and Lepadicyathus); and caudal skeleton with a single, large fan-like hypural plate (vs. caudal skeleton with upper and lower hypural plates, separated by narrow hypural diastema; Fig. 2A-D).
Etymology.-Combination of the new Latin flabellum, an anatomical term for a body organ or part that resembles a fan, and cauda, meaning tail. In reference to the unique shape of the hypural plate. Feminine.
Remarks.-Flabellicauda belongs to the subfamily Diademichthyinae, which was recently revised (''expanded'') by Conway et al. (2020) based on the shared presence of the following characters: upper-jaw teeth incisiviform, compressed laterally, with hooked tip; premaxillae separated anteriorly by large circular gap in dorsal view; and complex articulation present between posterior tip of basipterygium and anteromedial edge of ventral postcleithrum. The new genus shares several morphological characters in common with Lepadicyathus, including a similar arrangement of the cephalic sensory canal pores, features of the jaws (including a small mouth restricted to the anterior tip of snout; Fig. 1A H), and a restricted gill opening. The two genera are potentially closely related but are distinguished by characters listed in the diagnosis (warranting separate generic status), and detailed investigation of Lepadicyathus is currently ongoing (K. Fujiwara, unpubl.).
Though we have not investigated the phylogenetic relationships among the four species of Flabellicauda, based on our preliminary observations we recognize two putative monophyletic groups each comprising a pair of putative sister taxa. This includes: (1) F. alleni, new species, and F. bolini; and (2): F. akiko and F. cometes, new species. We consider the members of the first group to represent each other's closest relatives based on an almost identical external appearance (including an identical color pattern). The second pair comprises two miniature taxa (sensu Weitzman and Vari, 1988) that exhibit a number of reductive characters in relation to the other two members of the genus (including lower numbers of dorsal-and anal-fin rays, and the absence of the infraorbital lateral-line canal and associated pores, LC1 and LC2). Our investigation of cleared and stained material and CT datasets did not reveal any additional osteological characters in support of these two putative monophyletic groups, and further investigation of additional characters will be needed to corroborate or refute.
Coloration.-Based on Figures 3, 4A-E, 5, 8A-D. Body black with white stripe on dorsal midline (Fig. 5C) and three white stripes on each side (Fig. 5A, B, D); uppermost stripe extending from snout tip, past dorsal margin of pupil and pectoral fin, to caudal-fin base, its width very narrow on snout, gradually wider from head region, widest on body, slightly tapering posteriorly; central stripe narrowest of three stripes, extending from posterior point of lower jaw (or snout tip; Fig. 5A), passing below pupil, to pectoral-fin base, both tips tapering; lowermost stripe located ventrally, united in front of pelvic disc, forming large isosceles triangle shape, its tip located on ventral surface of snout tip (Fig. 5E), posterior tip of stripe tapering and reaching caudal-fin base, its width on body same as uppermost stripe; stripe on dorsal midline tapering posteriorly and extending from snout tip to dorsalfin origin; all stripes edged very faint yellow (sometimes distinct in life; Fig. 8A-C). Stripes of single individual from Philippines notably narrower than in other individuals (Fig.  8D). Iris black except for upper and lower portions, pupil black. Tubes of nostrils and all fins except for rays transparent, fin rays faint black. Adhesive disc white, isosceles triangle shape of black pigmentation at center, its tip located at anterior margin of disc (Fig. 5E).
Preserved coloration uniformly yellowish (Fig. 3). Black melanophores present on body of small specimens (ca. ,20 mm SL), those forming two stripes (somewhat indistinct in large specimens; Fig. 4A, B), upper and lower stripes located  dorsally and laterally, respectively, former extending from nape to most posterior point of dorsal-fin base, latter extending from pectoral-fin base to caudal-fin base ( Fig. 4A-E).
Description.-Measurements given in Table 4. Body slender, cylindrical, compressed at caudal peduncle. Body width narrower than head width. Anus situated closer to anal-fin origin than to posterior margin of disc (disc to anus length 63.4 [56.4-64.4] % of disc to anal-fin origin length). Head size medium, depressed anteriorly, its length and width 2.8 (2.7-2.9) and 5.3 (5.0-6.3) in SL, respectively. Snout moderate, its length 10.7 (10.9-12.3) in SL, its tip slightly pointed in lateral view, duck beak-shaped in dorsal view; dorsal profile of snout slightly concave anteriorly. Mouth terminal, small, restricted to tip of snout. Anterior tip of upper jaw slightly pointed, extending slightly beyond that of lower jaw. Upper lip fleshy, weakly expanded, lower lip thin. Posterior 2/3 of both jaws covered by thick skin on lateral surface of snout. Anterior and posterior nostrils larger than head sensory canal pores, former slightly smaller than latter; both with a membranous tube, that of former longer than latter. Eye size moderate, diameter slightly larger (slightly smaller in 2 specimens) than snout length, 10.6 (9.4-12.6) in SL. Interorbital region flattened. Gill opening tiny, slit-like. Upper end of gill opening level with base of 13 th (12 th or 13 th ) pectoral-fin ray in lateral view (number of pectoral-fin rays given in Table 2); lower 8 th (8 th [3 specimens] or 9 th [4]) pectoral-fin-ray base attached to disc by membrane. First to third gill arch with two rows of gill filaments, 4 th arch without filaments (gill description based on 3 specimens). Gill rakers slender, pointed and very short, somewhat indistinct (not visible in 1 of 3 specimens; gill raker counts listed in Table 3). Gill membranes on each side united ventrally, attached to isthmus. Head sensory canal pores poorly developed, including 2 nasal and 1 postorbital pore; lacrimal, preopercular, and mandibular pores absent; all pores similarly sized with minute membranous tube; NC1 located in front of anterior nostrils in dorsal view (or between anterior and posterior margins of anterior nostril); NC2 between anterior and posterior margins (before anterior margin [2 of 5 specimens] or level with anterior margin [1 specimen]) of posterior nostril; PO1 located just behind posterior margin of orbit (Fig. 6D-F).
Dorsal-and anal-fin-ray counts listed in Table 2. Origin of dorsal fin slightly anterior to vertical through anal-fin origin. Dorsal and anal fins located posteriorly, their bases relatively long, lengths 6.4 (4.4-6.7) and 7.0 (5.3-7.6) in SL, respectively; strongly connected to caudal fin by membranes, giving appearance of single, continuous median fin around posterior part of body (easily damaged). Post-dorsal-caudal length 3.3 (4.6-6.6) in dorsal-fin base length. Dorsal-and anal-fin heights almost equal, except anteriorly. Pectoral-and caudal-fin margins rounded. Pectoral-fin rays 27 (27 [2] or 28 [5]). Upper and lowermost pectoral-fin rays minute, longest ray extending beyond vertical through posterior margin of disc. All soft-fin rays unbranched. Principal caudal-fin rays segmented. Pelvic fins and pectoral-girdle elements forming a circular, extremely small ''single'' adhesive disc (Fig. 7B), its length and width 8.5 (8.3-9.0) and 8.0 (6.7-9.5) in SL, respectively. Disc region B bell-shaped, equal in size to disc region A. Anterior margin of disc region A smooth, posterior margin of disc region B with fringe. Disc regions A and B with  flattened papillae (disc papillae description based on 5 specimens). Center of disc region A lacking papillae; anterolateral part with 2 or 3 rows of papillae, number of rows slightly decreasing toward apapillate center; both sides of disc region A (except margins) covered with papillae; papillae of inner rows slightly larger than outer rows. Disc region B with 4 (5) rows of papillae; papillae of inner rows slightly larger than papillae of outer rows, anterior part of disc region B without papillae (Fig. 7B). Disc region C lacking papillae.
Coloration.-Based on Figure 16, fresh coloration described only from dorsal view (Fig. 16F). Body maroon with white stripe on dorsal midline and lateral side of body; stripe on dorsal midline extending from snout tip to dorsal-fin origin, its width broad anteriorly, gradually narrower toward posterior; lateral stripes extending from posterior point of jaws, past dorsal margin of eye, to posterior part of body (becoming indistinct posteriorly). Snout tip dark red, jaws reddish orange. Pupil black. Preserved coloration uniformly yellowish (Fig. 16A-E).
Distribution.-Known from the Indian Ocean (Seychelles and Chagos Archipelagoes) and western Pacific Ocean (Queensland, Australia, and Kiribati; Fig. 14).
Etymology.-From the Latin cometes, a comet, a reference to the bold white stripe along the dorsal midline, reminiscent of the trailing tail of a traveling comet against the night sky. A noun in apposition.
Remarks.-Our description of F. cometes is based only on eight individuals, collected from widely separate localities in the Indian and Pacific Oceans. We have chosen to tentatively identify this material as conspecific because we could not identify significant differences between specimens from these different localities. Additional investigation, including assessment of life colors (which was not possible for specimens from localities in the Pacific), is warranted.
Single row of small similarly sized teeth in both jaws; upperjaw teeth incisiviform, compressed laterally, with hook-like tips strongly curved posteriorly (ca. 908); lower-jaw teeth with pointed conical tips, inner surface slightly curved. Premaxillae separated anteriorly by large circular gap in dorsal view (based on radiographs of 1 specimen). Anterior and posterior nostrils larger than head sensory canal pores, former slightly smaller than latter; both with a membranous tube, that of former much longer than latter. Eye size slightly large, becoming smaller with growth (Fig. 9D), diameter slightly larger (slightly smaller in 7 specimens) than snout length, 14.3 (7.9-12.3 [10.3]) in SL. Interorbital region flattened. Gill opening tiny, slit-like. Upper end of gill opening level with base of 14 th (12 th to 14 th ) pectoral-fin ray in lateral view (number of pectoral-fin ray given in Table  2); lower 9 th (8 th [13 specimens] or 9 th [12]) pectoral-fin-ray base attached to disc by membrane. First to third gill arches with two rows of gill filaments, 4 th arch without filaments (gill description based on 26 specimens). Gill rakers slender, short and pointed (gill raker counts listed in Table 3). Gill membranes on each side united ventrally, attached to isthmus. Head sensory canal pores relatively developed, including 2 nasal, 2 (1 on left side only in 2 specimens) lacrimal, and 2 postorbital pores; preopercular and mandibular pores absent; all pores similarly sized with minute membranous tube; NC1 located in front of anterior nostrils in dorsal view (or between anterior and posterior margins of anterior nostril); NC2 before anterior margin (level with anterior margin [5 of 30 specimens], between anterior and posterior margins [18 specimens], or level with posterior margin [3 specimens]) of posterior nostril; LC1 located in front of anterior margin of eye; LC2 located just below LC1 (postero-ventrally below LC1 [18 of 29 specimens]); PO1 located just behind posterior margin of orbit; PO2 on slightly higher horizontal level of PO1 ( Fig. 19A-C). Dorsal-and anal-fin-ray counts listed in Table 2. Origin of dorsal fin slightly anterior to vertical through anal-fin origin. Dorsal and anal fins located posteriorly, their bases relatively long, lengths 5.3 (4.3-6.1 [5.1]) and 5.7 (4.7-6.6 [5.8]) in SL, respectively; strongly connected to caudal fin by membranes, giving appearance of single, continuous median fin around posterior part of body (easily damaged). Upper and lower hypural plates completely fused, forming single large fan-like hypural plate (radiographs of 10 specimens, not including holotype). Post-dorsal-caudal  disc. All soft-fin rays unbranched and segmented. Pelvic fins and pectoral-girdle elements forming a circular, extremely small ''single'' adhesive disc (Fig. 7C), its length and width 9.0 (8.3-11.3 [9.4]) and 10.2 (7.4-11.2 [9.5]) in SL, respectively. Disc region B bell-shaped, equal in size to region A. Anterior margin of disc region A smooth, posterior margin of disc region B with fringe. Disc regions A and B with flattened papillae (disc papillae description based on 12 specimens). Center of disc region A lacking papillae; anterolateral part with (2 or 3) rows of papillae, number of rows slightly decreasing toward apapillate center; both sides of disc region A (except margins) covered with papillae; papillae of inner rows slightly larger than papillae of outer rows. Disc region B with 5 (4 or 5) rows of papillae; papillae of inner rows slightly larger than outer rows, anterior part of disc region B without papillae (Fig. 7C). Disc region C lacking papillae.
Coloration.-Based on Figures 4F-J, 8E, 18. Body black with white stripes on dorsal midline and lateral side, stripe pattern very similar to those of F. alleni (see Coloration of F. alleni).
Preserved coloration uniformly yellowish (Fig. 18). Black melanophores present on body of small specimens (ca. ,16 mm SL), forming an upper and lower stripe (somewhat indistinct in large specimens; Fig. 4F, G); upper and lower stripes located dorsally and laterally, respectively, former extending from nape to most posterior point of dorsal-fin base, latter extending from pectoral-fin base to caudal-fin base (Fig. 4F-J).
Remarks.-Flabellicauda bolini was originally described as Lepadichthys bolini by Briggs (1962) on the basis of a single specimen (CAS 158341, 28.8 mm SL; Fig. 18A-C) collected from Vanuatu. Although this species has previously been considered to be widely distributed throughout the Indo-West Pacific by several authors (e.g., Briggs, 1969a;Winterbottom et al., 1989;, these previous records refer either to F. alleni or F. cometes (described    (Fig. 14).
In their book of the reef fishes of the East Indies, Allen and Erdmann (2012) included an underwater photograph of unidentified species of Lepadichthys taken at Papua New Guinea (Fig. 8E). Judging from its general appearance (e.g., mouth and vertical fins shape) and the locality, the photographed individual likely belongs to F. bolini.
Description.-Measurements given in Table 5. Body slender, cylindrical, compressed at caudal peduncle. Body width narrower than head width. Anus situated closer to anal-fin origin than to posterior margin of disc (disc to anus length 68.1 [65.5-68.6] % of disc to anal-fin origin length).
Vertebrae 34 (based on CT-scanned image of WAM P. 35180-001). Head size medium, depressed anteriorly, its length and width 2.8 (2.9-3.1) and 7.0 (6.3-7.1) in SL, respectively. Snout moderate, its length 9.4 (10.1-13.3) in SL, tip slightly pointed in lateral view, duck beak-shaped in dorsal view; dorsal profile of snout slightly concave anteriorly. Mouth terminal, small, restricted to tip of snout. Anterior tip of upper jaw slightly pointed, extending slightly beyond that of lower jaw. Upper lip fleshy, weakly expanded, lower lip thin. Posterior 2/3 of both jaws covered by thick skin on lateral surface of snout; thick skin of snout visible in dorsal and ventral view as obvious bulge posterolateral to mouth (skin only weakly expanded in 2 specimens; Fig. 20E, F). Single row of small similarly sized teeth in both jaws; upper-jaw teeth incisiviform, compressed laterally, with hook-like tips strongly curved posteriorly (ca. 908); lower- jaw teeth with pointed conical tips, inner surface slightly curved. Premaxillae separated anteriorly by large circular gap in dorsal view (based on CT-scanned image of WAM P. 35180-001). Anterior and posterior nostrils larger than head sensory canal pores, former slightly smaller than latter; both with a membranous tube, that of latter very short and somewhat indistinct. Eye size moderate, diameter slightly smaller (or larger in 2 specimens) than snout length, 11.2 (9.8-16.1) in SL. Interorbital region flattened. Gill opening tiny, slit-like. Upper end of gill opening level with base of 10 th (or 9 th ) pectoral-fin ray in lateral view (number of pectoral-fin ray given in Table 2); lower 6 th (6 th [1 specimen], 7 th [1] or 8 th [2]) pectoral-fin-ray base attached to disc by membrane. First to third gill arches with two rows of gill filaments, 4 th arch without filaments (gill description based on 2 specimens, not including holotype). Gill rakers slender, very short and pointed (gill raker counts listed in Table 3). Gill membranes on each side united ventrally, attached to isthmus. Head sensory canal pores poorly developed, including 1 nasal and 1 postorbital pore; preopercular, lacrimal, and mandibular pores absent; all pores similarly sized with minute membranous tube. Nasal pore located in front of anterior nostrils in dorsal view (or between anterior and posterior margins of anterior nostril). Postorbital pore just behind posterior margin of orbit ( Fig. 19D-F). Dorsal-and anal-fin-ray counts listed in Table 2. Origin of dorsal fin slightly anterior to vertical through anal-fin origin. Dorsal and anal fins located posteriorly, their bases relatively short, lengths 5.7 (4.6-7.0) and 6.7 (5.1-8.1) in SL, respectively; strongly connected to caudal fin by membranes, giving appearance of single, continuous median fin around posterior part of body (easily damaged). Upper and lower hypural plates fused, forming single large fan-like hypural plate (based on CT-scanned image of WAM P. 35180-001). Post-dorsal-caudal length 4.3 (2.5-6.3) in dorsal-fin base length. Dorsal-and anal-fin heights almost equal, except anteriorly. Pectoral-and caudal-fin margins rounded. Pectoral-fin rays 27 (26 [1] or 27 [3]). Upper and lowermost pectoral-fin rays minute, longest ray extending beyond vertical through posterior margin of disc. All soft-fin rays unbranched and segmented. Pelvic fins and pectoral-girdle elements forming a circular, extremely small, ''single'' adhesive disc (Fig. 7D), its length and width 8.9 (8.1-10.3) and 13.5 (9.5-11.2) in SL, respectively. Disc region B bellshaped, equal in size to disc region A. Anterior margin of disc region A smooth, posterior margin of disc region B with fringe. Disc regions A and B with flattened papillae (disc papillae description based on 3 specimens). Anterior part of disc region A with 3 rows of papillae across center; both sides of disc region A (except margins) covered with papillae; papillae of inner rows slightly larger than papillae of outer rows. Disc region B with 4 (4 or 5) rows of papillae; papillae of inner rows slightly larger than papillae of outer rows, anterior part of disc region B without papillae (Fig. 7D). Disc region C lacking papillae.
Coloration.-Based on Figures 8F-H, 20 and Fujiwara and Motomura (2018: figs. 1, 4). Body red with three broad white stripes on each side; upper and lowermost stripes continuing onto dorsal and ventral surface of head, respectively, visible in lateral view; uppermost stripe extending from snout tip, past dorsal margin of eye, to posteriormost point of dorsal-fin base, slightly tapering posteriorly; central stripe extending along side of body, from snout tip to caudal-fin base (or reaching center of caudal fin) through pupil, posterior third slightly expanded, tapering at posterior tip; lowermost stripe narrow (or somewhat indistinct), extending just below middle of eye to anterior margin of pelvic disc, both tips tapering; additional red stripe extending along ventral midline from posterior portion of pelvic disc to in front of anus. Slightly indistinct (distinct in life; Fig. 8F-H) bright white stripes on dorsal midline and between upper and middle red stripes. Upper and lower parts of iris white, pupil black. Tubes of nostrils, all fins, and pelvic disc transparent.
Distribution.-Currently known only from Okinawa Island, Japan (based on underwater photographs), Palau, and West Papua, Indonesia Fig. 14).
Remarks.-Flabellicauda akiko was originally described as Lepadichthys akiko by Allen and Erdmann (2012) on the basis of a single specimen (MZB 20592, 10.5 mm SL; Fig. 20A-C) collected from West Papua, Indonesia. Subsequently, Fujiwara and Motomura (2018) recorded the species from Palau and Okinawa Island, Japan and also provided additional information on gill raker counts and head sensory canal pores based on the examination of addition material, which they considered to be diagnostic characters for the species. Allen and Erdmann (2012) and  reported pectoral-fin ray counts of 16 or 17 and 18, respectively, for F. akiko, but our reexamination of their material has revealed the number of pectoral-fin rays to be higher (26 or 27). The lowermost rays of the pectoral fin are embedded inside of the fleshy membrane that unites the pelvic and pectoral fins and are easily overlooked.

DISCUSSION
Ecological notes on Flabellicauda.- Allen and Erdmann (2012) were first to provide information on the ecology of F. akiko, based on observations and photographs of a single individual discovered attached to a sponge over a rubble substrate at 70 m depth (this specimen later became the holotype; Allen and Erdmann, 2012; Fig. 8F). Subsequently,  suggested that F. akiko is likely epibenthic, based on underwater photographs taken at Okinawa Island (Japan) that captured an individual hovering in the water column in close proximity to a sea urchin (Fujiwara and Motomura, 2018: fig. 4). Additional underwater photographs of this species included herein (Fig. 8G, H) provide further documentation of this behavior. Underwater photographs of F. alleni and F. bolini reveal these two species also spend time hovering in the water column, in all cases amongst the spines of sea urchins of the family Diadematidae ( Fig. 8A E;37813,38041,73907,73908,84746; all KPM-NR pictures were here identified as F. alleni based on locality [Philippines or Malaysia]). Whether these two species also attach to the urchin spines that they shelter within is currently unknown as we are aware of only a single underwater photograph of F. alleni in which the photographed individual is attached to a substrate, in this case a rock in close proximity to a sea urchin (Fig. 8D). Though gobiesocids, especially reef-associated species, are frequently encountered in close proximity or attached to marine invertebrates, including sponges, corals, gorgonians, sea urchins, and crinoids (e.g., Craig and Randall, 2008: fig. 1; Craig et al., 2015: fig. 4;Fricke and Wirtz, 2017: figs. 4, 5;Conway et al., 2018b;Fujiwara et al., 2020: fig. 8), the majority of these taxa are benthic. To the best of our knowledge, the only other epibenthic gobiesocid is Diademichthys lineatus, which is frequently observed and photographed hovering in the water column between the spines of diadematid sea urchins (e.g., Randall et al., 1990: 56;Randall, 1995Randall, : 349, 2005Allen and Erdmann, 2012: 839). Based on the topology presented in Conway et al. (2020: figs. 3, 4), the epibenthic behavior exhibited by the members of Diademichthys and Flabellicauda is most likely the product of convergence. It is of note that members of both genera exhibit an extremely small adhesive disc, compared to close relatives, and this reduction in overall disc size may be related (in some way) to the epibenthic behavior of these species. Though we do not have information on the behavior of F. cometes, we expect that this species likely also is epibenthic. Another potential parallel between the ecology of Flabellicauda and Diademichthys is the consumption of the tube feet of sea urchins. Sakashita (1992) reported tube feet of sea urchins in the stomachs of adult D. lineatus, and also noted that large males (~40 mm SL) consume larger quantities of tube feet than smaller males and females. We removed two partially digested tube feet from the stomach of a single individual of F. alleni (FMNH 127786), suggesting that at least one of the species of Flabellicauda consumes tube feet, and potentially those of the sea urchins in which they seek shelter. Like the majority of gobiesocids, F. alleni, F. bolini, and F. cometes inhabit relatively shallow coastal waters, at depths of 0.6-23 m, 0.6-12 m, and 3-13 m, respectively. Notably, F. akiko occurs at much greater depths (40-90 m) than the other members of the genus and is one of only~20 species of gobiesocid known to inhabit depths greater than 50 m (see Hastings and Conway, 2017: table 1). Underwater observations of F. akiko by M. Erdmann (pers. comm.) confirm that this species is an inhabitant of mesophotic coral reefs (i.e., largely tropical, light-dependent communities found between 30-150 m depth; Loya et al., 2019). Gobiesocids are rarely encountered in mesophotic coral reef ecosystems, and in addition to F. akiko, other mesophotic coral reef-dwelling gobiesocids include the members of the new world genus Derilissus (which contains five species, D. altifrons, D. kremnobates, D. lombardii, D. nanus, and D. vittiger ;Briggs, 1969b;Fraser, 1970;Smith-Vaniz, 1971;Sparks and Gruber, 2012) and potentially also certain eastern tropical Atlantic members of the genus Diplecogaster (including D. ctenocrypta and D. tonstricula; Fricke et al., 2015).
Comments on diagnostic characters of Flabellicauda.-In the majority of gobiesocids, the caudal-fin skeleton includes a single large hypural complex or urostyler complex (e.g., see Monod, 1968;Springer and Fraser, 1976;Hayashi et al., 1986;Fujita, 1990;Konstantinidis and Conway, 2010). At the posterior edge of this complex, adjacent to the caudal-fin diastema, is a narrow opening or notch of variable length that divides the complex into an upper and lower part (upper and lower hypural plates of recent authors; e.g., see Conway et al., 2017b: fig fig. 3; Fig. 2C-H). Development of the caudal skeleton has not been investigated for gobiesocids, and it is unknown whether the single hypural element present in adults is derived from a single hypural cartilage or from multiple separate hypural cartilages that may undergo ontogenetic fusion. In the members of Flabellicauda, there is no narrow opening or notch at the center of the posterior part of the hypural complex, and the posterior edge is straight, giving the complex the overall appearance of a large triangular or fan-like element ( Fig. 2A, B), reminiscent of the condition in some members of the Atherinomorpha, in which only a single fan-like hypural element is present in adult individuals (e.g., see Parenti, 1981: fig. 2F; Ghedotti, 2000: fig. 17B; Costa, 2012: figs. 2B, 3B;Thieme et al., 2021: fig. 8i, k). A small circular opening is located at the center of the hypural complex of Flabellicauda, and this may be homologous to the anterior part of the narrow opening or notch that divides the hypural complex into an upper and lower part in other gobiesocids. If we are correct, the condition in Flabellicauda may represent a peramorphic condition in which the narrow opening or notch that is present in the hypural complex of other gobiesocids has become closed posteriorly, potentially via ontogenetic fusion. Though the condition of the hypural complex in Flabellicauda is unique amongst diademichthyine clingfishes, Springer and Fraser (1976) have documented a similar (convergent) condition in Alabes dorsalis, in which only a single fan-shaped hypural element is present, though in this case without a small opening at the center (see Springer and Fraser, 1976: fig. 7).
In addition to the shape of the hypural complex, the caudal region of Flabellicauda is also notable because of the connection between the three median fins. This connection is established by a thin, narrow membrane of skin spanning the short gap between the posteriormost ray of the dorsal or anal fin and the anteriormost dorsal or ventral procurrent ray of the caudal fin, respectively. This thin membrane is easily damaged during collection and preservation but persists in well-preserved material and gives the impression of a single, continuous median fin around the posterior part of body in the members of Flabellicauda. In the majority of gobiesocids, the dorsal and anal fins are separate from the caudal fin (see Briggs, 1955: figs. 82-101, 103-112;Fujiwara, 2019: 327, 329) or in the few other cases in which these fins are connected by a thin transparent membrane (see Briggs, 1955: figs. 102, 113, 114;Fujiwara, 2019: 327, 328), the median fins appear as separate entities because the gap between the posteriormost ray of the dorsal or anal fin and the anteriormost dorsal or ventral procurrent ray of the caudal fin is much greater than in Flabellicauda. In Gouania willdenowi, the gap between the caudal and dorsal/anal fins is bridged by a high number of procurrent rays, which are housed within the same ridge of thick skin that accommodates the greatly reduced dorsaland anal-fin rays (Konstantinidis and Conway, 2010). This arrangement also gives the external appearance of a single continuous median fin around the posterior part of the body, but this condition is different from the condition in Flabellicauda. Shiogaki and Dotsu (1983) considered the number and position of cephalic lateral-line canal pores as important characteristics for defining higher groups of gobiesocids, especially genera. We have also found characters of the cephalic lateral-line canal system useful for the purpose of diagnosing Flabellicauda relative to other genera of the Diademichthyinae and also for diagnosis of the different members of the genus. In all four species of Flabellicauda, the preoperculo-mandibular lateral-line canal is absent, and this character, in combination with others, is useful to distinguish the new genus from the other diademichthyine genera that possess this structure (e.g., the preopercle houses a canal in Aspasma, Diademichthys, Flexor, Lepadichthys, Pherallodichthys, and Propherallodus; Shiogaki and Dotsu, 1983;Conway et al., 2018a;Motomura, 2019b, 2020b). There is also variation in the infraorbital and otic lateral-line canal among the four members of Flabellicauda. In F. alleni and F. bolini, the infraorbital canal is represented by a poorly ossified tube on the lacrimal, with two canal openings (LC1 and LC2). In F. akiko and F. cometes, the infraorbital canal (and associated pores) is absent. The otic canal (and associated pore on the pterotic; PO2) is present in F. alleni, F. bolini, and F. cometes, but absent in F. akiko. The tiny F. akiko, the largest specimen of which is recorded at 14.0 mm SL, exhibits the greatest number of reductions to the cephalic lateral-line system of the four species of Flabellicauda, and these reductions may be the product of developmental truncation, associated with the evolutionary process of miniaturization (Weitzman and Vari, 1988;Hanken and Wake, 1993). Intraspecific variation is rarely documented for characters of the cephalic lateral-line system in gobiesocids but Hayashi and Hayashi (1985), , and Fujiwara and Motomura (2020b) have documented asymmetry in the number of cephalic lateral-line canal pores present on either side of the head for a small number of individuals. We have also recorded asymmetry in the number of pores in the nasal portion of the supraorbital canal, and the infraorbital canal of F. alleni, and the infraorbital canal of F. bolini (see Description). We did not observe asymmetry in the number of pores associated with the cephalic lateral-line canal system in F. akiko or F. cometes, but this may be related to the small number of specimens of each available for examination.
Comments on Lepadichthys.-In a recent molecular phylogenetic study of gobiesocids, Lepadichthys was identified as one of several non-monophyletic genera in need of taxonomic revision (Conway et al., 2020). As a first step towards this necessary revision, we have transferred two morphologically distinct species that have previously been considered members of Lepadichthys to our new genus Flabellicauda. We have taken this step because these two species (F. akiko and F. bolini) were inferred by Conway et al. (2020) to be more closely related to members of other diademichthyine genera than to other species of Lepadichthys (note that Conway et al.'s material of F. bolini actually represents F. alleni). Lepadichthys, as currently defined and adopting the taxonomic changes herein, now contains 12 species (viz. L. bilineatus, L. caritus, L. coccinotaenia, L. conwayi, L. ctenion, L. erythraeus, L. frenatus [type species], L. lineatus, L. minor, L. misakius, L. sandaracatus, and L. trishula), and the next step in the process of taxonomic revision will require us to assess: (1) whether these 12 species represent a monophyletic group or not; and (2) whether the morphological characters used to diagnose the genus in the last taxonomic revision (Briggs, 1955) are still useful for diagnosing this group or whether they need to be revised (as has been suggested previously; . This work is currently underway, and to date we have examined material representing 11 of 12 valid species of the genus (all except for L. bilineatus; see Material Examined).
Based on our preliminary morphological observations, we have identified what we consider to represent a ''core'' group of eight species that exhibit all the morphological characters used to diagnose the genus in the last revision (see Briggs, 1955;Fujiwara et al., 2020). This core group includes L. coccinotaenia, L. conwayi, L. ctenion, L. erythraeus, L. frenatus (type species), L. misakius, L. sandaracatus, and L. trishula. In addition to the morphological characters listed by Briggs (1955), these eight species also exhibit a well-developed lateral-line canal along the preopercle (with three pores) and similar mouth features (oral cleft moderate, not covered by skin, and snout tip not strongly pointed or protracted; Fig.  1B, G). We have not examined material of L. bilineatus but suspect, based on information provided in the original description (Craig et al., 2015), that this species is also a member of our core group. Although there is some evidence from a recent molecular phylogenetic study to suggest that this core group of Lepadichthys (as defined herein) may not be monophyletic (because L. misakius and L. trishula were not recovered as a monophyletic group; see Conway et al., 2020), and although we have not identified any putative derived characteristics that would provide an additional line of evidence to group these nine taxa together, we tentatively consider this core group of Lepadichthys to be monophyletic for the time being.
We do not consider the remaining three species of Lepadichthys (L. caritus, L. lineatus, and L. minor) to belong to this core group outlined above because they do not exhibit all of the diagnostic characters of Lepadichthys proposed by Briggs (1955), and also lack the preopercular lateral-line canal. For example, Lepadichthys lineatus and L. caritus do not exhibit the large circular opening between the premaxillae present in the core members of Lepadichthys (and also members of Flabellicauda and Lepadicyathus). As pointed out by previous authors (e.g., Hayashi and Hayashi, 1985;Craig and Randall, 2008), L. lineatus shares a number of features in common with the members of Discotrema, and is potentially more closely related to Discotrema than to the other members of Lepadichthys (as confirmed in the molecular phylogenetic study of Conway et al., 2020 in which L. lineatus is placed as a member of a clade that also includes Diademichthys lineatus and Discotrema crinophilum). Lepadichthys minor is known from relatively few specimens, but our preliminary observations of this miniature species (max recorded 21.8 mm SL) have revealed that it shares a number of characters in common with Flabellicauda and Lepadicyathus and is potentially more closely related to the members of these genera than to the members of the core group of Lepadichthys. Determination of the generic placement of these three 'outlier' species of Lepadichthys is beyond the scope of this paper but is forthcoming (K. Fujiwara, unpubl.).

DATA ACCESSIBILITY
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