JOURNAL OF CRUSTACEAN BIOLOGY, 21(2): 506–520, 2001 HETEROPOLYONYX BIFORMA, NEW GENUS AND SPECIES, FROM JAPAN, AND REDESCRIPTION OF POLYONYX UTINOMII (DECAPODA: PORCELLANIDAE) Masayuki Osawa Department of Zoology, National Science Museum, 3–23–1, Hyakunincho, Shinjuku-ku, Tokyo 169–0073, Japan (e-mail: [email protected]) ABSTRACT Heteropolyonyx, new genus (type species: H. biforma, new species), is established on the basis of the presence of transverse ridges on the cervical regions of the carapace and the telson being di- vided into five plates, characters quite different from its related genera Polyonyx Stimpson, 1858, and Eulenaios Ng and Nakasone, 1993. The male/female pair of H. biforma was found in a tube of an unidentified polychaete of the genus Chaetopterus. Polyonyx utinomii Miyake, 1943, is re- described from the holotype specimen and recently obtained material from Japan and the Mal- dives. This species is readily distinguishable from the other Indo-West Pacific species of Polyonyx by the carapace and chelipeds covered with numerous transverse and oblique striae on the dorsal surface and the meri of the chelipeds having a very large, broadly rounded lobe on the dorsoflexor margin. The present record of P. utinomii from the Maldives is the first report outside Japan and greatly extends its geographical distribution westwards into the Indian Ocean. The Polyonyx sinensis group, as recognized tified species of Chaetopterus. Through his by Johnson (1958), may be defined by a suite kind cooperation, I could examine the spec- of characters of the carapace, chelipeds, and imens and found that they belong to an un- dactyli of ambulatory legs, and is currently described species. This species resembles represented by 10 Indo-West Pacific species: members of the Polyonyx sinensis group in P. sinensis Stimpson, 1858; P. transversus general appearance, but differs from all (Haswell, 1882); P. pedalis Nobili, 1905; P. species of Polyonyx Stimpson, 1858, and its utinomii Miyake, 1943; P. loimicola Sankolli, relative Eulenaios Ng and Nakasone, 1993, 1965; P. maccullochi Haig, 1965; P. haigae in the structures of the cervical regions of the McNeil, 1968; P. vermicola Ng and Saseku- carapace and the telson. I herein describe the mar, 1993; P. plumatus Yang and Xu, 1994; specimens as a new genus and species. and P. bella Hsueh and Huang, 1998 (Ng and In addition, I include here a redescription Sasekumar, 1993; Yang and Xu, 1994; Hsueh of Polyonyx utinomii, a rarely recorded and Huang, 1998). Six members of the P. species of the P. sinensis group. This species sinensis group are known to be associated was originally described by Miyake (1943) with tube-dwelling polychaete worms be- based on a single specimen from Tanosaki longing to the genera Chaetopterus, Meso- (Tanabe Bay, Shirahama, Wakayama Prefec- chaetopterus, and Sasekumaria of the family ture, Japan) and the records are restricted to Chaetopteridae and Loimia of the Terebelli- just a few localities in Japan (Miyake, 1943; dae (see Miyake, 1965; Ng and Sasekumar, Miyake et al., 1962; Nakasone, 1978). Al- 1993; Hsueh and Huang, 1998). Of these host though the original description and figures re- genera, Sasekumaria was recently found to be vealed that the species was quite different a junior synonym of Mesochaetopterus by from the other Indo-West Pacific species of Nishi (1999). Polyonyx, a more detailed examination of the During a faunal research of cryptic deca- type specimen and additional material is pod crustaceans from Kushimoto, southern needed for evaluating the intraspecific varia- part of Wakayama Prefecture, Japan, by Mr. tions and more precise systematic relation- K. Nomura of the Yeayama Marine Park Re- ships with the allied species. I examined the search Station, a pair of unusual porcellanid holotype and recently obtained material from crabs was collected from a tube of an uniden- Japan and the Maldives and redescribe P. 506 OSAWA: HETEROPOLYONYX BIFORMA AND POLYONYX UTINOMII 507 utinomii in detail. The presence of this species tro-extensor margin; propodus elongate; ex- in the Maldives is the first record outside opod robust, without distal flagellum. Che- Japan and greatly extends its geographical lipeds unequal, subcylindrical, not showing distribution westwards into the Indian Ocean. distinct sexual dimorphism in shape; carpus The carapace length (CL) was measured unarmed; chela narrow; dactyl opening at from the anteromedian apex of the rostrum strongly oblique angle, not twisted. Ambula- to the posteromedian end of the carapace, and tory legs short, subcylindrical; merus without the carapace width (CW) at the broadest distinct decalcified region on mesial surface; point. Measurements of chelipeds and ambu- dactyl with bifurcate claw, flexor claw much latory legs follow those of Osawa (1998a). larger than extensor. Male with pair of de- The description presented includes the de- veloped pleopods on second abdominal tailed morphology of the ocular peduncle, somite; endopod with broadly rounded apex; thoracic sternites, antennular and antennal pe- no exopod; pleopods of female present only duncles, third maxilliped, and male pleopods. on fourth and fifth abdominal somites. Telson These structures have not been frequently de- composed of 5 plates; proximal lateral plates scribed for porcelain crabs in general, but can each with very shallow suture on proximal prove useful in systematic studies of the Por- part; distal plates of female much more cellanidae (see Kropp, 1986; Ng and Naka- strongly elongated than those of male. sone, 1994; Osawa, 1998b; Harvey, 1999). The holotype specimen of P. utinomii was Etymology.—This name is derived from the borrowed from the Seto Marine Biological Greek, heteros, meaning different, in combi- Laboratory, Kyoto University, Japan (SMBL), nation with the generic name Polyonyx. The and the additional material of that species and gender is masculine. the type specimens of the present new species are deposited in the Natural History Museum Type species.—Heteropolyonyx biforma, new and Institute, Chiba, Japan (CBM). species. SYSTEMATIC ACCOUNT Remarks.—Heteropolyonyx agrees with the Polyonyx sinensis species group of Johnson Family Porcellanidae Haworth, 1825 (1958) based on the morphological structures, Heteropolyonyx, new genus but is distinguished from this group and all Diagnosis.—Carapace, chelipeds, and ambu- other members of Polyonyx and its relative latory legs fringed with short and long Eulenaios by the following characters: (1) the plumose setae marginally. Carapace trans- carapace has a pair of transverse ridges along versely ovate; dorsal surface convex, regions the cervical regions; and (2) the telson is di- not well defined; protogastric ridges weakly vided into five plates, the distal two plates marked; cervical regions with no grooves, but of female are much more strongly elongated each with transverse ridge. Rostrum broad, than those of male. All the known porcellanid slightly bent ventrally, weakly produced and genera, including Polyonyx and Eulenaios, trilobate anteriorly; median lobe without lon- lack cervical transverse ridges on the cara- gitudinal groove. Pterygostomian flaps entire. pace. Polyonyx and Eulenaios have the telson Third thoracic sternite strongly depressed, composed of seven plates; the distal plates trilobate anteriorly; median lobe flattened, of female are rather short. In addition to the with longitudinal sulcus. Ocular peduncles two distinctions, Heteropolyonyx is distin- small. Basal segment of antennular peduncles guished from Eulenaios by the following fea- unarmed, slightly concave on anterior face. tures: (1) the regions on the carapace are not Antennal peduncles slender; first segment im- well defined in Heteropolyonyx, whereas they movable, strongly produced forward in lateral are very well defined and clearly demarcated view, broadly in contact with anterior mar- by the pattern of shallow and deep grooves in gin of carapace; second to fourth segments Eulenaios; and (2) the rostrum is broad and movable, excluded from orbit; third segment weakly produced anteriorly in Heteropoly- longest. Third maxillipeds with coxa bearing onyx, but it is rather narrow and strongly pro- distomedian projection incompletely articu- duced in Eulenaios. lated; basis articulated with ischium; ischium The proximal lateral plates of the telson of short, without longitudinal ridge along ven- Heteropolyonyx have a very shallow suture 508 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 21, NO. 2, 2001 on the proximal part, which is rather diffi- ridge extending to mesobranchial region; pos- cult to observe, especially on the male. Paul terior regions with short and long oblique ru- et al. (1993) described the juvenile morphol- gae bearing plumose setae anteriorly. Ros- ogy of two porcellanids, Petrolisthes trum (Fig. 1D) not produced beyond eyes; rufescens (Heller, 1861) and Pisidia gordoni median lobe broadly rounded, slightly ex- (Johnson, 1970), and revealed that the divi- ceeding and broader than laterals; lateral sion of the telson plates started in the juve- lobes each with broadly rounded apex. Orbits nile phase and developed from proximal to (Fig. 1J, K) very shallow; supraorbital mar- distal (see their Fig. 2p for Petrolisthes gins oblique, unarmed; outer orbital angles rufescens, Fig. 4q for Pisidia gordoni). Fol- rounded. Frontal region slightly depressed, lowing their results, the division of the prox- with very short striae or small pit and minute imal lateral plates of the telson of Het- setae as in hepatic regions.