A new genus and new species of deep-water trapeziid crab (Crustacea: Decapoda: Brachyura: Trapezioidea) from the Ryukyu Islands, Japan Author Komai, Tomoyuki Author Higashiji, Takuo Author Castro, Peter text Zootaxa 2010 2555 62 68 journal article 10.5281/zenodo.196907 75a8fe9a-5028-4a6a-ba3c-aa404344d072 1175-5326 196907 Hexagonaloides bathyalis n. sp. [new Japanese name: Shinkai-sango-gani] ( Figs. 1–3 ) Material examined. Holotype : male (3.8 × 5.5 mm ), off Ie Island , Okinawa, Ryukyu Islands (Okinawa Prefecture), 26°36.947’N , 127°44.092’E , 247 m , on a rock entangled in gill net, coll. T. Higashiji, CBM-ZC 9935. Paratype : 1 male (3.7 × 5.1 mm ), same data as holotype , CBM-ZC 9936. Description . Holotype . Carapace ( Figs. 1 , 2 A) hexagonal in outline, about 1.4 times wider than long; dorsal surface slightly convex longitudinally and transversely, microscopically granular, smooth. Front about half of greatest width of carapace, nearly straight medially, sloping slightly laterally in dorsal view. Orbit lacking fissures; supraorbital margin concave in dorsal view, lateral angle slightly produced, unarmed; suborbital margin weakly granular, inner suborbital angle bluntly triangular, not reaching front, antennular flagellum entering orbit. Lateral margin convex with small acute tooth at midlength, anterolateral margin very slightly arcuate, posterolateral margin nearly straight or very slightly convex; posterior margin subequal to width between outer orbital angles, with very shallow excavation laterally. Pterygostomial region ( Fig. 2 B) nearly smooth, a shallow groove extending from anterolateral angle of buccal frame. Buccal frame not narrowed anteriorly; epistome very narrow, with 2 rounded lobes either side of broadly triangular median lobe. FIGURE 1 . Hexagonaloides bathyalis n. gen. , n. sp. , holotype, male (3.8 × 5.5 mm), CBM-ZC 9935. Entire animal in dorsal view. FIGURE 2. Hexagonaloides bathyalis n. gen. , n. sp. , holotype, male (3.8 × 5.5 mm), CBM-ZC 9935. A, carapace and cephalic appendages, dorsal view; B, frontal region and cephalic appendages, left side, anterior view; C, left third maxilliped, outer view; D, third to fifth thoracic sternites, ventral view; E, details of median part of fifth to seventh thoracic sternites, ventral view; F, abdomen, outer view; F, left first gonopod, ventral (sternal) view; G, left second pleopod, ventral (sternal) view; I, same, different view. Scale bars: 1 mm for A–F; 0.5 mm for G–I. FIGURE 3. Hexagonaloides bathyalis n. gen. , n. sp. , holotype, male (3.8 × 5.5 mm), CBM-ZC 9935. A, left major cheliped, dorsal view; B, same, chela, outer view; C, right minor cheliped, dorsal view; D, same, chela, outer view; E, left fourth pereopod (third ambulatory leg), posterior view; F, same, dactylus, posterior view; G, same, obliquely flexor view, showing flexor surface; H, left fifth pereopod (fourth ambulatory leg), posterior view; I, same, dactylus, posterior view. Scale bars: 2 mm for A, C; 1 mm for B, D, E, H; 0.5 mm for F, G, I. Eye ( Fig. 2 A, B) not concealed in orbit when retracted; cornea slightly narrower than eyestalk. Antennular peduncle ( Fig. 2 A, B) with first segment transversely oval. Antennal peduncle ( Fig. 2 A, B) standing obliquely in frontal view. Interantennular septum broadly triangular, depressed. Third maxilliped ( Fig. 2 C) moderately wide; ischium widened proximally, with prominent projection distally on mesial margin, broadly rounded proximomesial margin; merus smaller than ischium, with small triangular process on distal margin, forming articulation with carpus; dactylus slightly longer than propodus, tapering distally; exopod moderately stout, inner mesial margin with triangular process subdistally; flagellum well developed. Chelipeds ( Figs. 1 , 3 A–D) unequal, slightly dissimilar, surface smooth to naked eye, but microscopically granular, sparsely setose. Larger (left) cheliped about 1.9 carapace length, not massive; merus with blunt, minutely granular anterior ridge, largely visible in dorsal view; dorsodistal margin spinulose in inner half. Carpus short, lacking tooth at inner angle. Chela 2.7 times as long as deep. Palm elongate, depth slightly increasing distally; dorsal and ventral surfaces rounded; ventral margin in outer view slightly sinuous; fixed finger slightly deflexed, terminating in curved, acute tip, cutting edge thin, sinuous, minutely dentate. Dactylus 0.7 times as long as palm, weakly curved, minutely granular on dorsal margin, terminating in acute tip crossing tip of fixed finger; cutting edge thin, minutely granular. Smaller (right) cheliped about 1.7 of carapace length; merus bearing clearly granular anterior ridge. Chela 3.0 times as long as deep. Fixed finger with cutting edge nearly straight except for curved tip, bearing 3 nearly indistinguishable teeth proximally. Dactylus 0.9 times as long as palm, terminating in curved, acute tip, crossing tip of fixed finger, cutting edge non dentate. Ambulatory legs ( Figs. 1 , 3 E–I) long, slender, smooth to naked eye, sparsely setose; similar in structure, third leg longest; dactylo-propodal lock well developed. Propodi each with flexor margin bearing row of slender movable spinules on distal half. Dactyli subequal in length to propodi, weakly curved, each terminating in minute corneous spinule; extensor surfaces each with slender short spiniform setae arranged in 3 irregular rows in distal 0.4–0.5 portion; flexor surface narrowly channeled, flanked by thin, crenulated edges, each edge with 8–11 slender corneous spinules. Thoracic sternum broad. Third and fourth sternites ( Fig. 2 D) fused, forming large plate, anterior margin broadly convex with median point, short suture between third and fourth sternites. Fifth sternite with tuft of short setae on either side of midline; press button very small, papilla-like ( Fig. 2 D, E). Sixth sternite with short transverse row of setae on either side of midline ( Fig. 2 E). Gonopore coxal, but located close to eighth sternite. Male abdomen ( Fig. 2 F) with third to fifth somites incompletely fused, sutures clearly delimited in lateral sides. Third somite widest. Telson ( Fig. 2 F) triangular, nearly as long as wide, with proximolateral corner rounded. First gonopod ( Fig. 2 G) reaching to suture between fourth and fifth sternites, curved at proximal 0.3; distal 0.6 slender, gently curved dorsally, parallel to midline, gradually tapering to acute tip; row of minute spiniform setae directed laterally on distal 0.25 of lateral margin. Second gonopod ( Fig. 2 H, I) short, about 0.3 length of first gonopod, slightly curved ventrally; tip obliquely truncate. Paratype . Similar to holotype . Coloration in life . Body and appendages pale pink, bases of fingers and palms of chelipeds darker. Corneas grayish. Remarks . The two specimens are small, but the well-developed gonopods clearly suggest that they are not juveniles. Etymology . Named in reference to the deep-water habitat of the new species.