Flabellicauda, Fujiwara & Conway & Motomura, 2021

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 : 754-756

Flabellicauda , new genus urn:lsid:zoobank.org:act:D5DF20D1-F059-49BF-8E98-DD526FD103A1

Type species.— Flabellicauda alleni , new species.

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.

Included species.— The genus contains four valid species: F. akiko , F. alleni , new species, F. bolini , and F. cometes , new species.

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.

Figures

FIG. 1. Lateral view of heads of (A) Flabellicauda alleni, new species, WAM P. 35182-001, preserved specimen, 21.4 mm SL; (B) Lepadichthys frenatus, AMS I. 20256-013, preserved specimen, 35.3 mm SL; (C) Diademichthys lineatus, KAUM-I. 79654, 26.4 mm SL; (D) Discotrema crinophilum, KAUM-I. 72122, 26.3 mm SL; (E) Lepadichthys lineatus, KAUM-I. 128500, 22.0 mm SL; (F) Lepadichthys minor, KAUM-I. 70995, 18.2 mm SL; (G) Lepadichthys trishula, KAUM-I. 71567, 31.1 mm SL; and (H) Lepadicyathus mendeleevi, ZIN 53413, preserved holotype, 13.5 mm SL.

FIG. 2. Caudal skeletons of (A) Flabellicauda alleni, new species, FMNH 127786, 17.1 mm SL; (B) Flabellicauda cometes, new species, ROM 55928, 10.3 mm SL; (C) Lepadichthys frenatus, AMS I. 27134-018, 30.3 mm SL; (D) Lepadichthys minor, ROM 73449, 13.4 mm SL; (E) Discotrema crinophilum, ROM 85350, 25.4 mm SL; (F) Diademichthys lineatus, ROM 65282, 35.6 mm SL; (G) Gobiesox funebris, AMNH 5557, 46.7 mm SL; and (H) Acyrtus rubiginosus, UF 149202, 20.0 mm SL. Scale bars ¼ 1 mm. Abbreviations: AFR, anal-fin ray; DFR, dorsal-fin ray; DRC, cartilaginous distal radial; Ep, epural; EpC, epural cartilage; HP, hypural plate; HSPU2, hemal spine of preural centrum 2; LHP, lower hypural plate; NSPU2, neural spine of preural centrum 2; Ph, parhypural; PhC, parhypural cartilage; P-MR, proximalmiddle radial; PU, preural centrum; UC, ural centrum; and UHP, upper hypural plate. Asterisks indicate diastema between UHP and LHP.