Flabellicauda akiko ( Allen and Erdmann, 2012 )

Fujiwara, Kyoji, Conway, Kevin W. & Motomura, Hiroyuki, 2021, 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, Ichthyology & Herpetology 109 (3), pp. 753-784 : 773-778

Flabellicauda akiko ( Allen and Erdmann, 2012)

Minute Clingfish

Figures 7D , 8F–H , 14 , 15 , 19 , 20 ; Tables 1–3, 5

Lepadichthys akiko — Allen and Erdmann, 2012: 1164, figs. 1–3 (original description; type locality: east of Point Mangguar, Cenderawasih Bay, West Papua, Indonesia); Fujiwara and Motomura, 2018: 88, figs. 1–5 (description; Okinawa Island, Japan [based on underwater photographs] and Palau [BPBM 37695, 37705]); Conway et al., 2020: 893, figs. 3, 4 (molecular result; East Kalig Island, Misool, Raja Ampat, Indonesia: based on WAM P. 35180-001).

Holotype.— MZB 20592 , 10.5 mm SL, east of Point Mangguar , Cenderawasih Bay, West Papua, Indonesia, 02825 0 50 00 S, 134859 0 25 00 E, 70 m, M. Erdmann, 20 September 2010, clove oil.

Non-type specimens.— 4 specimens, 11.1–14.0 mm SL. Indonesia: WAM P. 33772-002, 11.5 mm SL, same as type locality, 44–45 m, M. Erdmann, 15 June 2012 ; WAM P. 35180-001, 11.1 mm SL, East Kalig Island , Misool, Raja Ampat, 02813 0 15 00 S, 130833 0 14 00 E, ca. 60 m, M. Erdmann, 16 June 2015 . Palau: BPBM 37695 , 14.0 mm SL, Augulpelu Reef , 07816 0 24.6 00 N, 134831 0 26.4 00 E, ca. 90 m, J. Earle, 10 May 1997 ; BPBM 37705 , 12.3 mm SL, same locality as BPBM 37695, ca. 90 m, R. Pyle and J. Earle, 12 May 1997 .

Diagnosis.— A species of Flabellicauda ( Fig. 20 ) distinguished from congeners by the following unique 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 and F. bolini ; 2 nasal pores present in F. cometes ; Fig. 19 ); upper end of gill opening level with base of 9 th or 10 th pectoral-fin ray in lateral view (vs. 12 th to 14 th); disc region A with papillae at center (vs. disc region A without papillae at center; Fig. 7 ); and body red with white stripes (vs. body black or maroon with white stripes; Fig. 8F–H ). In addition to the aforementioned diagnostic characters, F. akiko also exhibits a slightly narrower head (head width 14.1–16.0% SL), and slightly narrower anterior and posterior interorbital widths (7.6–8.3%, and 11.7–14.0% SL, respectively) when compared with congeners of similar body size ( Fig. 15 ). A small number of meristic and morphometric characters also distinguish F. akiko from congeners (see Diagnosis of F. alleni and 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 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 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.

Preserved coloration uniformly yellowish (or whitish; Fig. 20 ), body stripes indistinct, orangish or yellowish (disappearing completely after several years in preservative: Fujiwara and Motomura, 2018: fig. 1; Fig. 20 ).

Distribution.— Currently known only from Okinawa Island, Japan (based on underwater photographs), Palau, and West Papua, Indonesia ( Fujiwara and Motomura, 2018; 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 Fujiwara and Motomura (2018) 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.

Figures

FIG. 7. Pelvic discs of (A) F. alleni, new species, USNM 360264, holotype, 26.2 mm SL; (B) F. cometes, new species, ROM 55929, holotype, 17.3 mm SL; (C) F. bolini, ANSP 128248, 20.6 mm SL; and (D) F. akiko, WAM P. 33772-002, 11.5 mm SL. Scale bars ¼ 0.5 mm. Black dots indicate lacking disc papillae patch.

FIG. 8. Underwater photographs of (A–D) F. alleni, new species, (E) F. bolini, and (F–H) F. akiko. (A–C) 1.5 m depth, Rinca Island, West Flores, Indonesia. Photos by M. Erdmann. (D) 7 m depth, Bohol, Philippines. Photo by K. Yamasaki. (E) 5 m depth, Manus, Papua New Guinea. Photo by G. Allen. (F) 70 m depth, West Papua, Indonesia. Holotype. Photo by G. Allen. (G) 70 m depth, West Papua, Indonesia. Photo by M. Erdmann. (H) 40 m depth, Okinawa Island, Japan. Photo by N. Shirakawa. (A–E, G, H) Specimens not collected. (E, F) Reproduced from Allen and Erdmann (2012) with permission.

FIG. 14. Distributional map of species of Flabellicauda: F. alleni, new species (red diamonds), F. cometes, new species (yellow squares), F. bolini (blue circles), and F. akiko (green triangles). Closed and open symbols indicate records based on specimens examined in this study and published photographs, respectively. Arrowheads indicate type locality.

FIG. 15. Relationships of (A) caudal-peduncle length, (B) caudal-peduncle depth, (C) caudal-peduncle length plus caudal-peduncle depth, (D) head width, (E) anterior interorbital width, and (F) posterior interorbital width (as % of SL) in F. alleni, new species (red diamonds), F. cometes, new species (yellow squares), F. bolini (blue circles), and F. akiko (green triangles).

FIG. 19. Head sensory canal pores of (A–C) Flabellicauda bolini and (D–F) Flabellicauda akiko. Illustrations based on (A–C) ANSP 128248, 20.6 mm SL and (D–F) WAM P. 33772-002, 11.5 mm SL. (A, D) Dorsal views. (B, E) Lateral views. (C, F) Ventral views. Scale bars ¼ 1 mm. Abbreviations as in Figure 6.

FIG. 20. Preserved specimens of Flabellicauda akiko. (A–C) MZB 20592, holotype, 10.5 mm SL, West Papua, Indonesia; (D–F) WAM P. 33772-002, 11.5 mm SL, West Papua, Indonesia. (A, D) Lateral views. (B, E) Dorsal views. (C, F) Ventral views.