Zootaxa, A new genus and new species of deep ...

TERMS OF USE This pdf is provided by Magnolia Press for private/research use. Commercial sale or deposition in a public library or website is prohibited. Zootaxa 2555: 62–68 (2010) www.mapress.com / zootaxa/

ISSN 1175-5326 (print edition)

Article

Copyright © 2010 · Magnolia Press

ZOOTAXA ISSN 1175-5334 (online edition)

A new genus and new species of deep-water trapeziid crab (Crustacea: Decapoda: Brachyura: Trapezioidea) from the Ryukyu Islands, Japan TOMOYUKI KOMAI1, TAKUO HIGASHIJI2 & PETER CASTRO3 1

Natural History Museum and Institute, Chiba, 955-2 Aoba-cho, Chuo-ku, Chiba, 260-8682 Japan.E-mail: [email protected] Okinawa Churaumi Aquarium, 424 Ishikawa, Motobu, Okinawa, 905-0206 Japan. E-mail: [email protected] 3 Biological Sciences Department, California State Polytechnic University, Pomona, California 91768–4032, USA. E-mail: [email protected] 2

Abstract A new genus and new species of trapeziid crab, Hexagonaloides bathyalis, is described from Okinawa, Ryukyu Islands (Okinawa Prefecture), Japan, on the basis of two male specimens collected at a depth of 247 m. The new genus is unique among the Trapeziidae in having a combination of the hexagonal carapace bearing a single lateral spine and a smooth frontal margin and the unarmed anterior margin of the cheliped meri. The symbiotic association of the new taxon remains unknown. Key words: Crustacea, Decapoda, Brachyura, Trapeziidae, new genus, new species, Ryukyu Islands

Introduction The eubrachyuran family Trapeziidae Miers, 1886, consists almost exclusively of coral symbionts, occurring in the Indo-West Pacific and Tropical Eastern Pacific regions. A recent revision (Castro et al. 2004) listed all the recognized genera and species and stabilized the nomenclature. Six genera, Trapezia Latreille, 1828 (type genus), Quadrella Dana, 1851, Hexagonalia Galil, 1986, Calocarcinus Calman, 1909, Philippicarcinus Garth & Kim, 1983 and Sphenomerides Rathbun, 1897, are assigned to Trapeziidae. The Okinawa Churaumi Aquarium sampled deep-water fauna around Okinawa, Ryukyu Islands, using various methods, including gill nets on steep slopes below 200 m. Among the decapod crustaceans collected in the latter method were two specimens of an undescribed trapeziid. While superficially resembling species of Hexagonalia and Quadrella, some similarities to Calocarcinus and Philippicarcinus were observed as well. Consequently, a new monotypic genus, Hexagonaloides, is established to accommodate the new species, H. bathyalis. The specimens were found on a rock entangled in the gill net, so its possible host remains unknown. The specimens examined in this study are deposited in the collection of the Natural History Museum and Institute, Chiba (CBM). The measurements provided, in millimeters, are of the carapace length and width (including lateral teeth) respectively.

Systematics Superfamily Trapezioidea Miers, 1886 Family Trapeziidae Miers, 1886 Subfamily Quadrellinae Števčić, 2005

62

Accepted by S. Ahyong: 4 Jul. 2010; published: 2 Aug. 2010

TERMS OF USE This pdf is provided by Magnolia Press for private/research use. Commercial sale or deposition in a public library or website is prohibited.

Hexagonaloides n. gen. [new Japanese name: Shinkai-sanngo-gani-zoku] Type species. Hexagonaloides bathyalis n. sp.

Diagnosis. Carapace hexagonal; frontal margin smooth; anterolateral margins each with conspicuous, anterolaterally directed tooth arising at midlength. Orbit not concealing eye when retracted; supraorbital border lacking fissures. Chelipeds unequal; meri long, lacking teeth on anterior margin. Dactyli of second to fifth pereopods (first to fourth ambulatory legs) ending in small acute corneous spine, flexor margin bi-edged, each edge crenulate, with slender corneous spinules. Male abdomen with third to fifth somites incompletely fused (suture present laterally), although completely immobile. Male first gonopod slender, tapering to acute tip; second gonopod about 0.3 length of first gonopod, stout. Composition. Monotypic. Remarks. The new genus agrees well with the diagnosis of the Trapeziidae given by Castro et al. (2004). The entire frontal margin of the carapace and the lack of teeth on the anterior margin of the meri of chelipeds place this new genus close to Calocarcinus and Philippicarcinus. Hexagonaloides, however, is readily distinguished from these two genera by the shape of the carapace, the structure of the orbit and the form of the male gonopods. The carapace is hexagonal in the new genus, octagonal with parallel, straight sides along the middle portion in Calocarcinus (Castro et al. 2004: pl. 4C), and transversely ovoid in Philippicarcinus (Castro et al. 2004: pl. 4D). The lateral margin of the carapace bears one tooth in Hexagonaloides and Phlippicarcinus, and two teeth in Calocarcinus. The orbit is open, with the inner suborbital angle not reaching to the lateral angle of the front in the new genus, whereas it is closed with the inner suborbital angle reaching to the lateral angle of the front in the latter two genera. The first gonopod is more slender in Hexagonaloides than in Calocarcinus and Philippicarcinus, but the second gonopod is very short, about 0.3 the length of the first gonopod in Hexagonaloides, rather than notably elongated in Calocarcinus (see Serène 1984: figs. 197– 200) and Philippicarcinus (see Garth & Kim 1983: fig. 14c, d). Furthermore, the chelipeds and ambulatory legs are distinctly more slender in Hexagonaloides than in Calocarcinus and Philippicarcinus. In the shape of the carapace and the elongated chelipeds and ambulatory legs Hexagonaloides resembles Hexagonalia (see Castro et al. 2004: pl. 4B) and Quadrella (see Castro et al. 2004: pl. 4A), but the new genus is readily distinguished from the latter two genera by its smooth frontal margin and the anteriorly unarmed cheliped meri. In Hexagonalia and Quadrella the frontal margin bears acute teeth and the anterior margin of the cheliped meri is armed with a row of spine-like teeth. Furthermore, Hexagonalia differs from Hexagonaloides in having two teeth on the anterolateral margin of the carapace. Spheromerides (see Castro et al. 2004: pl. 4E) shares a smooth frontal margin with Hexagonaloides, but the possession of two lateral teeth and spinose cheliped meri clearly sets them apart. Finally, Trapezia differs from the new genus in having a trapezoidal carapace and dentate cheliped meri (Castro et al. 2004: pl. 2C, D). Within the Trapeziidae sensu Castro et al. (2004), Ng et al. (2008) recognised three subfamilies, Trapeziinae Miers, 1886, Calocarcininae Števčić, 2005, and Quadrellinae Števčić, 2005, citing differences in habitat, carapace and pereopodal features, as well as larval characters. This classification was followed by De Grave et al. (2009). It is not easy to decide on the subfamilial affiliation of the new genus, because its mixture of diagnostic features fits both Calocarcininae and Quadrellinae. We provisionally assign the new genus to Quadrellinae because of the similarities in the carapace shape and the proportionately longer ambulatory legs. Further collections should reveal any possible symbiotic associations, and future investigations on larval development and molecular markers would be helpful in determining its position. Among calocarcinines, Calocarcinus species are symbionts of deep-water ahermatypic corals and other colonial cnidarians, Philippicarcinus appears to be associated with deep-water glass sponges (P. K. L. Ng, personal communication) and Sphenomerides is not known to be associated with any particular hosts. Among quadrellines, species of Quadrella are symbionts of shallow-water antipatharians, gorgonians, alcyonaceans and, in one species, of shallow-water ahermatypic corals, while Hexagonalia species are symbionts of deepwater stylasterid (hydrozoan) corals and gorgonians (Castro et al. 2004; Castro 2005) . Etymology. From the generic name Hexagonalia and the suffix -oides (Latin) (= like, resembling), in reference to the superficial resemblance of the new genus to Hexagonalia. Gender: masculine.

NEW GENUS AND SPECIES OF TRAPEZIID CRAB FROM JAPAN

Zootaxa 2555 © 2010 Magnolia Press ·

63


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, 2A) 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. 2B) 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.

64

· Zootaxa 2555 © 2010 Magnolia Press

KOMAI ET AL.


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.



65


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.

66


KOMAI ET AL.


Eye (Fig. 2A, B) not concealed in orbit when retracted; cornea slightly narrower than eyestalk. Antennular peduncle (Fig. 2A, B) with first segment transversely oval. Antennal peduncle (Fig. 2A, B) standing obliquely in frontal view. Interantennular septum broadly triangular, depressed. Third maxilliped (Fig. 2C) 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, 3A–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, 3E–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. 2D) 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. 2D, E). Sixth sternite with short transverse row of setae on either side of midline (Fig. 2E). Gonopore coxal, but located close to eighth sternite. Male abdomen (Fig. 2F) with third to fifth somites incompletely fused, sutures clearly delimited in lateral sides. Third somite widest. Telson (Fig. 2F) triangular, nearly as long as wide, with proximolateral corner rounded. First gonopod (Fig. 2G) 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. 2H, 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.

Acknowledgments We sincerely thank Yukinobu Taira, the captain of the fishing boat Koufuku-maru and the staff in charge of the Deep-Sea Animal Section of the Okinawa Churaumi Aquarium, for their generous help in the field. Our sincere thanks are also extended to two reviewers for valuable suggestions for improvements of the



67


manuscript. The second author wishes to thank the Director Senzo Uchida, and chief of the staff Keiichi Sato and Atsushi Kaneko (Okinawa Churaumi Aquarium) for their encouragement.

References Castro, P. (2005) A new species of Hexagonalia (Crustacea: Brachyura: Trapeziidae) from the Solomon Islands. Proceedings of the Biological Society of Washington, 118, 539–542. Castro, P., Ng, P.K.L. & Ahyong, S.T. (2004) Phylogeny and systematics of the Trapeziidae Miers, 1886 (Crustacea: Brachyura), with the description of a new family. Zootaxa, 643, 1–70. De Grave, S., Pentcheff, N.D., Ahyong, S.T., Chan, T-Y, Crandall, K.A., Dworschak, P.C., Felder, D.L., Feldmann, R.M., Fransen, C.H.J.M., Goulding, L.Y.D., Lemaitre, R., Low, M.E.Y., Martin, J.W., Ng, P.K.L., Schweitzer, C.E., Tan, S.H., Tshudy, D. & Wetzer, R. (2009) A classification of living and fossil genera of decapod crustaceans. Raffles Bulletin of Zoology, Supplement 21, 1–109. Garth, J.S & Kim, H.S. (1983) Crabs of the family Xanthidae (Crustacea: Brachyura) from the Philippine Islands and adjacent waters based largely on collections of the U. S. Fish Commission steamer Albatross in 1908–1909. Journal of Natural History, 17, 663–729. Ng, P.K.L., Guinot, D. & Davie, P.J.F. (2008) Systema Brachyurorum: Part I. An annotated checklist of extant brachyuran crabs of the world. Raffles Bulletin of Zoology, Supplement, 17, 1–286. Lai, J.C.Y., Ahyong, S.T., Jeng, M.-S. & Ng, P.K.L. (2009) Are coral-dwelling crabs monophyletic? A phylogeny of the Trapezioidea (Crustacea: Decapoda: Brachyura). Invertebrate Systematics, 23, 402–408. Serène, R. (1984) Crustacés Décapodes Brachyoures de l’Océan Indien Occidental et de la Mer Rouge. Xanthoidea: Xanthidae et Trapeziidae. Addendum: Carpiliidae et Menippidae par A. Crosnier. Faune Tropicale (ORSTOM), 24, 1–400, pls. 1–48.

68


KOMAI ET AL.