CRUSTACEAN RESEARCH, NO. 25: 54-58, 1996

A new record of Pinnotheres bidentatus Sakai, 1939 (Decapoda: Brachyura: Pinnotheridae), from Taiwan

Pan-Wen Hsueh and Jung-Fu Huang

Abstract. — The pea crab Pinnotheres this crab species. bidentatus Sakai, 1939, previously known only from the type locality of Wakayama, Pinnotheres bidentatus Sakai, 1939 Japan, is recorded for the first time from (Figs. 1 A-J, 2A, B) a coastal area in west central Taiwan. Its Pinnotheres bidentatusSakai, 1939: 591, fig. swimming ability and color patterns on 78a-c (Wakayama, Japan); 1976: 572, fig. the dorsal carapace are also noted. 311a-c (no new locality); Silas and Alagarswami, 1967 (catalogued); Serene, Introduction R., 1968 (catalogued); Schmitt et al., 1973 (catalogued); Miyake, S., 1982 Pinnotheres bidentatus was first de- (catalogued). scribed by Sakai (1939) on the basis of one male and three females. These specimens Material. — 1 male, NMNS 2129-157, were collected from the coast of carapace length (cl.) 3.2 mm, carapace Wakayama, Japan. No other data was width (cw.) 3.8 mm; 2 adult females, provided by Sakai (1976) and the biology NMNS 2129-154, cl. 3.5 mm, cw. 4.1 mm and ecology of this species is virtually un- and NMNS 2129-156, cl. 3.2 mm, cw. 3.8 known. mm; 1 subadult female, NMNS 2129-155, In early 1993, three specimens of an cl. 3.6 mm, cw. 4.3 mm, in tidal waters unidentified pea crab were collected from over Kaomei tidal flats, Taichung County, a sandy mud habitat on the coastal wet- west central Taiwan, coll. P.-W. Hsueh, lands of Kaomei, Taichung County, Tai- November- December 1994. wan (24°39'N, 120°35'E). In the fall of Description. — Carapace subcircular, 1994, numerous individuals (n=2254, size upper surface convex and smooth, antero- ranged 1-4 mm carapace width) of the lateral and postero-lateral margins same species were collected from water rounded. Small hallows present at frontal columns at the same area during flooding and brachial regions of dorsal carapace tides in a survey of brachyuran and anterior thoracic sternum. Front megalopae. The identity of this pea crab markedly depressed, its margin with a was eventually determined as central tooth from anterior view. Orbits Pinnotheres bidentatus. In this study, we small, subcircular. Eyestalks short and report a new record for this species with thick, its diameter as broad as eyes. An- some notes on its biology. Four represen- tennule obliquely transverse; antenna tative specimens collected in fall of 1994 small, protruded from inner orbits. Buccal are used for the redecription, and they are frame crescentic, convergent at anterior deposited at National Museum of Natural part; cavity completely closed by external Science, Republic of China (NMNS Cat. # maxillipeds. Ischium and merus of exter- 2129-154 to 157). The other specimens nal maxillipeds fused, only with indistin- are kept by the first author for further guishable groove, to form a single piece. analysis on the population dynamics of Palp of external maxillipeds three jointed, A NEW RECORD OF PINNOTHERES BIDENTATUS FROM TAIWAN 55

Fig. 1. Pinnotheres bidentatus Sakai, 1939; A, dorsal view; B, anterior view; C, right chela; D, 4th ambulatory leg; E, 1st pleopod of male; F, external maxilliped; G, H, I, abdomen of female; J, abdomen of male. (A, H, female, cl. 3.2 mm, cw. 3.8 mm, NMNS 2129-156; B, C, D, F, I, female, cl. 3.6 mm, cw. 4.3 mm, NMNS 2129-155; E, J, male, cl. 3.2 mm, cw. 3.8 mm, NMNS 2129-157; G, female, cl. 3.5 mm, cw. 3.8 mm, NMNS 2129-157; Scale line = 1 mm) inserted at inner side of propodus. Cheli- length; merus of 2nd and 3rd ambulatory peds symmetrical and stout in both sexes; legs with short hair along its anterior dorsal and outer surface of carpus and margin, carpus and propodus with a row manus with a large number of small and of setae on the dorsal surface. Outer sur- rounded hollows; inner margin of move- face of ambulatory legs with small hol- able finger with two teeth, one basal and lows. Abdomen of female oval shape, with the other subdistal, and also with setae. the 4th segment widest in length; the 7th The 4th ambulatory leg shortest in segment varied from triangular to semi- Fig. 2. Pinnotheres bidentatus Sakai, 1939: A. dorsal view of male, cl. 3.1 mm, cw. 3.8 mm; B. closed-up view of the same specimen. A NEW RECORD OF PINNOTHERES BIDENTATUS FROM TAIWAN 57 circular shape. First male pleopod curved face intentionally in the laboratory. Crab outward at the middle part, with a long sinks into water when the water's surface setae at subdistal surface, and tapering at tension is interrupted. distal end.

Color. — Eyes reddish; carapace Acknowledgments greenish with yellow spots scattered on Comments and references provided by the entire dorsal area; a strip of dark pig- Drs. Peter K. L. Ng, Austin B. Williams ment extended from front toward back and an anonymous reviewer greatly im- margins of the carapace and become a proves the quality of this manuscript. The large elliptic spot at the heart area (Fig. Natural Museum of Natural Science is 2); ventral view whitish. appreciated for providing logistic support. This study is also partial funded by Remarks. — Numerous individuals of grants of the National Science Council, Pinnotheres bidentatus with various sizes Republic of China (grant # NSC84-2311- (1 to 4 mm in carapace width) and both B-178-004 to PWH and grant # NSC85- sexes were collected at the coastal habi- 2321-B-022-002 A16 to JFH). tats of mid-western Taiwan, indicating (1) the presence of P. bidentatus population at these areas although there are only 4 Literature Cited specimens known to the world previously, Christensen, A. M., & McDermott, J. J., 1958. (2) female crabs of this species may not Life-history and biology of the oyster crab, Pinnotheres ostreum Say. Biological necessary behaving as its congeners — Bulletin, Woods Hole, 114: 146-179. commensal in bivalves, (3) they may Hartnoll, R. G., 1972. Swimming in the hard emerge into water columns during flood- stage of the pea crab, Pinnotheres pisum ing tides and, presumably, buried to sub- (L.). Journal of Natural History, 6: 475- strata during ebb tides, since the 480. watermargin retreats up to 3 km from the Miyake, S., 1982. Japanese crustacean deca- pods and stomatopods in color. Vol. I. shoreline at this time. Macrura, Anomura and Stomatopoda. Swimming ability of P. bidentatus ap- Hoikusha Publishing Co., Osaka, 261 pp. pears to be good in both sexes. Individuals Pearce, J. B., 1966. The biology of the mussel are often seen swimming voluntarily for crab, Fabia subquadrata, from the waters of the San Juan Archpelago, Washington. several minutes in container in the labo- Pacific Science, 20: 3-35. ratory. When swimming, they bend their Sakai, T., 1939. Studies on the crabs of Japan. chelae slightly inward and hold the first IV. Brachygnatha, Brachyrhyncha. and fourth walking legs stationary in an Yokendo, Tokyo, pp. 365-741. inverted V-shaped, and fast stroking both , 1976. Crabs of Japan and the Adjacent side of the second and third walking legs Seas. In three volumes; English text, pp. xxix+773pp., Japanese text, pp. 1-461, back and forth sequentially. This swim- Plates volume, pp. 1-16, pis. 1-251. ming behavior of pea crab is also reported Kodansha, Tokyo, pp. 572-573. in several species in Pinnotherinae Schmitt, W. L., McCain, J. C., & Davison, E. S. (Stauber, 1945; Christensen and 1973. Decapoda I, Brachyura I, Family McDermott, 1958; Pearce, J. B. 1966; Pinnotheridae. In: H. E. Gruner & L. B. Holthuis, (eds.), Crustaceorum Catalogus, Hartnoll, R. G. 1972.). The swimming 3: 1-160. Dr. W. Junk B. V.-Den Haag. mechanisms of P. bidentatus is similar to Serene, R., 1968. The Brachyura of the Indo its congeners, P. pisum, described by Pacific Region. In: Prodromus for a check Hartnoll (1972). Apparently, P. list of the Non-planctonic Marine Fauna of bidentatus is too small to break the South East Asia. Singapore National Academy of Science, Special Publication, water's surface tension and re-submerged No.l: 33-120. itself when it is brought to the water sur- Silas, E. G., & Alagarswami, K, 1967. On an 58 P.-W. HSUEH & J.-F. HUANG

instance of parasitisation by the pea-crab parasitic on the American oyster Ostrea {Pinnotheres sp.) on the backwater clam (Gryphaea) virginica. Biological Bulletin, [Meretrix casta (Chemnitz)] from India, Woods Hole, 88: 269-291. with a review of the work on the systematics, ecology, biology and ethology of pea crabs of the genus Pinnotheres Addresses: (PWH) Department of Zoology, Latreille. In: Proceedings of the National Chung Hsing University, 250 Kuo Symposium on Crustacea held at Kuang Rd., Taichung, Taiwan ROC; (JFH) De- Ernakulam from January 12 to 15, 1965, partment of Aquaculture, National Kaohsiung Part III, Symposium Series 2, pp. 1161- Institute of Marine Technology, Kaohsiung, 1227. Marine Biological Association of Taiwan ROC. India, Marine Fisheries P. O., Mandapam E-mail: (PWH) [email protected]. Camp, India. edu.tw Stauber, L. A., 1945. Pinnotheres ostreum,