(Crustacea: Hymenosomatidae), from Okinawa, the Ryukyu Islands, Japan!

A New Hymenosomatid Crab, Elamenops;s ok;nawaens;s, n. sp. (Crustacea: Hymenosomatidae), from Okinawa, the Ryukyu Islands, Japan!

YUKIO NAKASONE 2 AND MAsATSUNE TAKEDA 3

ABSTRACT: A new species of the Hymenosomatidae (Crustacea, Brachyura), Elamenopsis okinawaensis Nakasone & Takeda, n. sp., is described on the basis of two specimens (male and female) from the Aha River, on Okinawa in the Ryukyu Islands. It is easily distinguished from its congeners, E. octagonalis (Kemp), E. hirtirostris Lucas & Davie, and E. mangalis Ng, by the different structure ofthe male abdomen, the dactyli ofthe walking legs, and the male first pleopod.

The family Hymenosomatidae has been repre Elamenopsis okinawaensis Nakasone & sented by five genera in Japan: Halicarcinus, Takeda, n. sp. Elamena, Trigonoplax, Rhynchoplax, and Figure 1 Neorhynchoplax (Sakai 1938, 1976, Miyake HOLOTYPE: Male (NsMT-Cr 11352), cw (car 1983). Ofthem, Rhynchoplax Stimpson, 1858, apace width) 4.1 mm, Aha River, Okinawa, and Neorhynchoplax Sakai, 1938, were treated Ryukyu Isands, Y. Nakasone & H. Hayashi, as synonyms ofHalicarcinus White, 1846, and leg., 7 August 1990. PARATYPE: One female Elamenopsis A. Milne Edwards, 1873, respec (NsMT-Cr 11353), cw 3.5 mm, same data as tively, in the excellent review by Lucas (1980). holotype. Thus, Japanese hymenosomatid crabs cur DIAGNOSIS: Carapace subcircular, each lat rently are represented by four genera. eral carapace wall with a forward-directed Recently, two specimens (male and female) spine above base offirst walking leg. Rostrum were found during ecological and distribu with 3 separate triangular lobes; median lobe tional research on decapod crustaceans from longest and below lateral ones. Chelipeds not the river mouth to the upper stream in Aha elongate, subequal, with a subterminal tooth River, in the northern part ofOkinawa in the on lower margin of merus. Walking legs very Ryukyu Islands. The collection point was on long, not laterally compressed; merus with a the left bank about 500 m upstream from the terminal spine; dactylus slender and curved river mouth, becoming tideland at low tide, distally, with one subterminal tooth. Male with muddy coarse sand and pebbles. The abdomen with segments 3-5 fused. Male first male and female specimens were collected pleopod slender, with row of setae on sternal together inside a 0.5 by 0.5 m quadrat. side. The specimens referred to Elamenopsis dif DESCRIPTION: Carapace subcircular, sur fer not only from the Japanese species, E. face smooth, with well-marked gastric, car ariakensis (Sakai, 1969), but also from all diac, and branchial regions; cervical and other representatives of the genus. In this gastrocardiac grooves deep; lateral carapace paper, we describe them as a new species, E. wall with a forward-directed spine above base okinawaensis. The specimens are deposited in of first walking leg. Front consisting of 3 the National Science Museum, Tokyo (NSMT). separate triangular lobes fringed with short setae, the median one longest and below the lateral two; postocular lobe small and sub acute, visible in dorsal view. Basal antennular I Manuscript accepted 25 June 1993. segment without lateral tooth and strong 2 Biological Laboratory, College of Education, Uni versity of the Ryukyus, Okinawa 903-01, Japan. angle. Third maxilliped with long setae on 3 Department ofZoology, National Science Museum, inner margin of ischium and merus, with Shinjuku, Tokyo 169, Japan. plumose setae on their outer margins; exo- 158 FIGURE I. Elamenopsis okinawaensis, D. Sp., holotype male: A, dorsal view; B, carapace; C, cheliped merus and carpus; D, left chela; E, left first walking leg; F, abdomen; G, left first pleopod. Scale = 2.0 mm for A-F; 0.2 mm for G. 160 PACIFIC SCIENCE, Volume 48, April 1994 gnath slender. Chelipeds not elongated, sub men. Y.N. acknowledges a grant for short equal, and much stouter than walking legs; term study abroad from the Ministry ofEduca merus with a subterminal tooth ventrally; tion, Science, and Culture of Japan. We are propodus smooth, and fingers as long as palm; grateful to Peter K. L. Ng and Christina cutting edges of both fingers with some de T. N. Chuang for their valuable comments on veloped irregular teeth. Female cheliped with the draft and for use ofequipment and space, out a subterminal tooth on ventral margin of especially during Y.N.'s stay in the Depart merus. Walking legs long and slender, setose; ment of Zoology, the National University of merus with a terminal spine; dactylus curved Singapore. distally, with only a subterminal tooth, with out recurved teeth along ventral margin. Male abdomen with segments 1 and 2 short, seg ments 3-5 fused without sutures; telson LITERATURE CITED rounded distally, suture between telson and fused segments visible. First pleopod slender, KEMP, S. 1917. Notes on Crustacea Decapoda distally curved toward sternum, with row of in the Indian Museum. X. Hymenosoma setae on sternal side distally. Female abdomen tidae. Rec. Indian Mus. (Calcutta) 13: with segments 1 and 2 short, segments 3-5 243-279. fused, forming major part ofabdomen; telson LUCAS, J. S. 1980. Spider crabs of the short and broad. family Hymenosomatidae (Crustacea: Bra REMARKS: Elamenopsis okinawaensis, n. sp. chyura) with particular reference to Aus resembles E. octagonalis (Kemp, 1917) from tralian species: Systematics and biology. India in having similar carapace regions, the Rec. Aust. Mus. 33: 148-247. presence of a spine on the lateral carapace LUCAS, J. S., and P. J. F. DAVIE. 1982. Hy wall, a subterminal tooth on the lower margin menosomatid crabs of Queensland estua ofthe chelipedal merus (Lucas 1980: 194), and ries and tidal mud flats, including descrip absence ofa spinule with a subterminal tooth tions of four new species of Elamenopsis on the ventral margin of each walking leg A. Milne Edwards and a new species of dactylus. However, it is distinguished from E. Amarinus Lucas. Mem. Queensl. Mus. 20: octagonalis by lacking short hairs on the 401-419. carapace, lacking a strong lateral tooth on the MIYAKE, S. 1983. A taxonomic list of bra basal antennular segment (Lucas 1980: 194), chyuran crabs from Japan. Pages 193 and having a different-shaped male first 249 in Japanese crustacean decapods and pleopod (Lucas & Davie 1982: 404). The new stomatopods in color. Vol. II. Brachyura species differs from E. hirtirostris Lucas & (crabs). Hoikusha Publishing Co., Ltd., Davie, 1982, from Queensland in having a Osaka. different regional pattern of the carapace, a NG, P. K. L. 1988. Elamenopsis mangalis sp. different shape of the male first pleopod, and nov., a new species of mangrove-dwelling lacking the spinules on the ventral margins of hymenosomatid crab from Singapore (De the walking leg dactyli. The new species is capoda, Brachyura). Crustaceana (Leiden) easily distinguished from E. mangalis Ng, 55: 274-278. 1988, from Singapore by the different regional SAKAI, T. 1938. Studies on the crabs of pattern of the carapace, the fusion of male Japan. III. Brachygnatha, Oxyrhyncha. abdominal segments 3-5 (3 and 4 in E. Pages 193-364, 22 pis. Yokendo Co., mangalis male), and the different shape ofthe Tokyo. male first pleopod. ---. 1969. Two new genera and twenty two new species ofcrabs from Japan. Proc. BioI. Soc. Wash. 82:243-280. ACKNOWLEDGMENTS ---. 1976. Crabs of Japan and the adja We are indebted to M. Irei and Christina cent seas. Vol. I, xxix + 773 pp; Vol. 2, T. N. Chuang for drawing the holotype speci- 16 pp, 251 pis. Kodansha Ltd., Tokyo.