Crustacean Research 2020 Vol.49: 49–55 ©Carcinological Society of Japan. doi: 10.18353/crustacea.49.0_49 A new species of Hexapinus Manning & Holthuis, 1981 (Decapoda: Brachyura: Hexapodidae) from Hatoma Island, Ryukyu Islands, Japan Tohru Naruse Abstract.̶ A new species of Hexapinus (Hexapodidae) is described from Hatoma Island, Ryukyu Islands, Japan. Hexapinus patuma, new species, is morphologically close to H. latus Rahayu & Ng, 2014, but can be distinguished by the structures of the carapace and third maxilliped, as well as the degree of setation of ambulatory legs. LSID urn:lsid:zoobank.org:pub:5743D245-C07D-4953-920A-CD781534F1F3 Key words: Taxonomy, new species, burrower, sandy bottom, yabbie pump ■ Introduction scribes one new species of Hexapinus Manning & Holthuis, 1981, collected from Hatoma Is- Systematics of the family Hexapodidae land, Yaeyama Islands, Ryukyu Islands, Japan. Miers, 1886, have been substantially revised Material examined is deposited in the Ryukyu by Manning & Holthuis (1981) and Rahayu & University Museum, Fujukan (RUMF), Uni- Ng (2014), and recent studies have added more versity of the Ryukyus, Japan. Measurements, new taxa (Ng & Rahayu, 2015; Velip & Riv- in millimetres, are indicated as carapace length onker, 2014; Rahayu & Widyastuti, 2018; Ng (CL)×carapace width (CW). Other abbrevia- & Wong, 2019); the family currently contains tions used in this paper are as follows: G1, 2, 44 recent species in 16 genera. Among these male first and second gonopod; mxp3, third taxa, eight species in five genera have been re- maxilliped; P2–4, second to fourth pereopods, corded from Japan: Hexalaughlia orientalis respectively. (Rathbun, 1909), Hexapinus latipes (De Haan, 1835), H. simplex Rahayu & Ng, 2014, Hexa- ■ Taxonomy plax megalops Doflein, 1904, Mariaplax che- nae Rahayu & Ng, 2014, M. narusei Rahayu & Family Hexapodidae Miers, 1886 Ng, 2014, M. ourabay Rahayu & Ng, 2014, Hexapinus Manning & Holthuis, 1981 and Rayapinus maenosonoi Rahayu & Ng, Hexapinus patuma, new species 2014 (De Haan, 1835; Matsuo, 1971; Sakai, LSID urn:lsid:zoobank.org:act:47005568- 1939; 1965; 1976; Rahayu & Ng, 2014; Naruse D106-429C-A989-6979C60B5944 et al., 2017). [New Japanese name: Patuma-mutsuashi-gani] Recent field work by the author collected a (Figs. 1–4) good number of hexapodids, including unde- scribed species, from subtidal environments Material examined with the help of SCUBA and yabbie pump (see Holotype, RUMF-ZC-5835, male, 4.9× Naruse et al., 2017). The present study de- 9.5 mm, in SE reef of Hatoma Island, Yaeyama Received: 27 Mar 2020. Accepted: 5 Apr 2020. Published online: 9 May 2020. 49 TOHRU NARUSE Fig. 1. Dorsal habitus of Hexapinus patuma, new species. A, holotype male, RUMF-ZC-5835, 4.9×9.5 mm; B, paratype female, RUMF-ZC-5836, 4.6×8.7 mm. A and B are isometric. Islands, Ryukyu Islands, Japan, 24.457048, orbital margin forming triangular inner orbital 123.833223, ca. －15 m, by SCUBA and yab- tooth; lower part of suborbital and entire ptery- bie pump, coll. T. Naruse, Y. Fujita, Y. Endo & gostomial and hepatic regions granulated, se- N. Yoshitake, 16 Sep. 2015. Paratype, RUMF- tose, anteromesial part of pterygostomial re- ZC-5836, 1 female, 4.6×8.7 mm, same data as gion with obliquely arranged costae (Fig. 2). holotype. Milne-Edwards’ opening distinct (Fig. 2). Ex- ternal orbital corner not angular, anterolateral Comparative material margin confluent to orbit just below external See Naruse et al. (2017). orbital corner; anterolateral margin entire, con- vex anterolaterally, posterolateral margin Description slightly concave anteriorly, divergent posterior- Carapace (Fig. 1) trapezoidal, CW 1.89–1.94 ly. Posterior margin long, lateral ends roundly times CL, dorsal surface convex strongly lon- concave, accommodating small condyle of tho- gitudinally, weakly transversely, smooth, re- racic sternite 7 (Fig. 1). gions indiscernible. Front sloping downwards, Epistome posterior margin forming wide medially concave in dorsal view but ventrally concave curvature, with weak median projec- produced to triangular lobe, forming part of in- tion. terantennular septum in frontal view. Supra-, Basal antennular article set transversely. An- infraorbital margins entire, mesial end of infra- tennal articles set obliquely, entering into orbit. 50 Crustacean Research 49 HEXAPINUS PATUMA, NEW SPECIES, FROM THE RYUKYUS Fig. 2. Anteroventral view of cephalothorax of Hexapinus patuma, new species. A, holotype male, RUMF-ZC-5835, 4.9×9.5 mm; B, paratype female, RUMF-ZC-5836, 4.6×8.7 mm. Abbreviations: l, pleonal locking mechanism; mo, Milne Edwards’ opening; mx3b, basis of third maxilliped; mx3f, flagellum of third maxilliped; s2/3, suture between thoracic sternites 2 and 3; s3/4, suture between thoracic sternites 3 and 4; v, vulva. Crustacean Research 49 51 TOHRU NARUSE Fig. 3. Hexapinus patuma, new species. A–E, holotype male, RUMF-ZC-5835, 4.9×9.5 mm; F, paratype female, RUMF- ZC-5836, 4.6×8.7 mm. A, third maxilliped, left (setae are partially drawn); B, male pleon and posterior margin of carapace (setae are not drawn); C, G1, left, ventral view; D, G1, left, dorsal view; E, G2, left, dorsal view; F, female pleon and posterior margin of carapace (setae are not drawn). Scales: 1 mm. Eyes relatively short, small, mobile. of ischium when folded. Exopod stout, mesial Mxp3 (Figs. 2, 3A) covering almost entire margin strongly convex, with long flagellum. buccal cavern. Basis with triangular projection Chelipeds of both sexes (Fig. 1) short, rela- mesially. Ischium short, shorter than merus, tively stout, stronger, asymmetric in male, sub- posterior margin strongly concave, mesial mar- equal in female. Right cheliped of male holo- gin strongly protruded, border with merus sinu- type (Figs. 1A, 4A) larger than that of left ous. Merus forming parallelogram. Palp long, (Figs. 1A, 4B). Male chelipeds merus short, dactylus longest among palp segments, reach- trigonal in cross-section, carpus rhomboidal, ing posterior to proximal half of mesial margin inner corner blunt, no tooth, upper surface 52 Crustacean Research 49 HEXAPINUS PATUMA, NEW SPECIES, FROM THE RYUKYUS Fig. 4. Hexapinus patuma, new species. Holotype male, RUMF-ZC-5835, 4.9×9.5 mm. A, right major chela; B, left minor chela; C, lower side of pereopods, showing mats of velvety setae. A and B are isometric. smooth; inner margins of merus, carpus lined dus and dactylus flexor surface to entire anteri- with setae; chela outer surface smooth, setose or surface, P4 proximal half of flexoanterior on upper half of inner surface of palm and in- margin; P4 carpus to dactylus flexor margin ner surface of movable finger and base of im- lined with long setae. Merus subrectangular; movable finger. Male major chela (Fig. 4A) carpus, propodus short, both subtriangular; with proportionally longer palm than minor dactylus acicular, extensor margin straight, ter- chela, fingers tip pointed; immovable finger minated in corneous claw. occlusal margin with low, wide, rounded sub- Male thoracic sternites 1, 2 (Fig. 2A) fused, medial tooth, subproximal tooth very small; triangular, medially depressed; sternites 2, 3 movable finger strongly curved downward dis- demarcated by thick ridge, laterally produced tally, occlusal margin with triangular tooth sub- anteriorly; sternites 3, 4 fused medially, demar- medially; minor chela (Fig. 4B) with pointed cated only by lateral notches; sternites 4–7 fingers tip; immovable finger occlusal margin very wide; sternopleonal cavity narrow, ster- with two small teeth subproximaly, followed nites 4–7 fused medially, no suture meeting distally by low lamellar blade; movable finger medially, cavity reaching to level of about occlusal margin similar to that of immovable proximal third of bases of cheliped coxae, an- finger, except for absence of second subproxi- teriorly and anterolaterally with 1 longitudinal mal tooth. Female chelal fingers similar to and 1 pair of oblique grooves, respectively, tip those of male minor chela. of G1 visible from oblique groove even when Ambulatory legs (Figs. 1, 4C) relatively pleon closed; pleonal locking button present on short, stout, P3 longest; mat of velvety setae suture 4/5 at lateral slope of cavity; lateral mar- present on following parts of P2–4 (Fig. 4C): gins of cavity sinuous, anterolateral corner of P2 merus flexor surface (except for distomedi- sternite 5, 6 produced, corresponding to lateral an part near articulation with carpus) to flexor projection of pleonal somites 6, 5, respectively. side of posterior surface, carpus flexor surface, Penis sternal. Female sternopleonal cavity (Fig. propodus flexor surface to flexor side of anteri- 2B) continued anteriorly as narrow groove as or surface, P3 merus flexor surface (except for far as sternite 3; anterolateral part at pleonal distomedian part near articulation with carpus) cavity of sternite 5 with triangular projection, to flexor side of posterior surface, carpus flexor functioning as pleonal locking mechanism; surface to almost entire anterior surface, propo- vulva (Fig. 2B) semicircular, directed mesio- Crustacean Research 49 53 TOHRU NARUSE ventrally. mesial margin, relatively shorter and stouter Male pleon (Figs. 2A, 3B) narrow; somites 1, P2–4, and distinctively more slender and elon- 2 short; somites 3–5 fused, laterally produced gate male pleon. Rahayu & Ng’s (2014) male on proximal fifth and distal third; somite 6 lat- characters are mainly based on that of H. sim- erally produced on proximal half; telson sub- plex Rahayu & Ng, 2014, which are subse- pentagonal, lateral margin concave, distally quently confirmed by the examination of a rounded. G1 (Fig. 3C, D) relatively stout, gen- male specimen of H. latipes (De Haan, 1835) tly curved outward, distal part abruptly bent (see Ng & Rahayu, 2015), the type species of outward, tapering to sharp tip. G2 (Fig. 3E) the genus. The G1 of H. latipes and H. simplex small, distal segment narrow, long. are similar in their slender and gently outward- Female pleon (Fig. 3F) spade-like, all so- curved shape throughout the length (Ng & Ra- mites free; somites 3, 4 widest; somite 6 lon- hayu, 2015: fig. 6A, B; Rahayu & Ng, 2014: gest, laterally convex on proximal half, inner fig.