A NEW DEEP-SEA CRAB OF THE GENUS CHACEON (DECAPODA, GERYONIDAE) FROM THE SOUTH CHINA SEA BY PETER K.L. NG Department of Zoology, National University of Singapore, Kent Ridge, Singapore 0511, Republic of Singapore DING-AN LEE Taiwan Fisheries Research Institute, 199 Ho-Ih Road, Keelung, Taiwan, Republic of China and HSIANG-PING YU Graduate School of Fisheries, National Taiwan Ocean University, Keelung, Taiwan, Republic of China ABSTRACT A new species of deep-sea crab, Chaceonmanningi (Brachyura, Geryonidae), is described from depths of 438 to 636 m in the Tung-Sa Islands, South China Sea. The dorsal carapace surface of C. manningiresembles C. granulatus from Japan but in the form of the anterolateral margin and ambulatory dactylus, C. manningiis closer to C. bicolorfrom New Caledonia, Australia, and New Zealand. Seven species of Chaceonare now known from the Pacific Ocean. Chaceonmanningi isthe largest member of the genus known so far. RÉSUMÉ Une nouvelle espèce de crabe d'eau profonde, Chaceonmanningi (Brachyura, Geryonidae), est décrite de 438 à 636 m, aux îles Tung-Sa, mer de Chine méridionale. La surface dorsale de la carapace de la nouvelle espèce ressemble à celle de C. granulatus,du Japon, mais par la forme du bord antéro-latéral et le dactyle des pattes ambulatoires, elle est plus proche de C. bicolorde Nouvelle-Calédonie, Australie et Nouvelle-Zélande. Sept espèces de Chaceonsont maintenant connues du Pacifique. Chaceonmanningi est le plus grand représentant du genre connu jusqu'à présent. INTRODUCTION The deep-sea geryonid crab genus Chaceon Manning & Holthuis, 1989, contains six known species from the Pacific Ocean: C. granulatus (Sakai, 1978), C. bicolor Manning & Holthuis, 1989 (New Caledonia, Australia, Loyalty Islands), C. yaldwyni Manning, Dawson & ?Vebber, 1989 (New Zealand), C. imperialis Manning, 1992 (Emperor Seamount Chain), C. poupini Manning, 1992 (Marquesas Islands), and C. karubar Manning, 1993 (Tanimbar Islands, Indonesia). 372 In 1991, the R/V "Hai-Kung" (700 tonnes) of the Taiwan Fisheries Research Institute obtained a series of deep-sea crabs from the Tung-Sa Islands in the South China Sea at depths between 438 to 636 m using deep-water bottom trawl nets. Two of the specimens proved to belong to an undescribed species of Chaceon Manning, & Holthuis, 1989. The description of this species, Chaceon manningi sp. nov., forms the basis of the present paper. The abbreviations cw and cl refer to the carapace width and length, respec- tively. Specimens are deposited in the Zoological Reference Collection (ZRC), Department of Zoology, National University of Singapore; and the crustacean collection of the National Taiwan Ocean University (NTOU), Taiwan, Repub- lic of China. '1'AXONOMI(; PART Geryonidae Chaceon Manning & Holthuis, 1989 ChaeeonManning & Holthuis, 1989: 51 (type species Geryora fenraer-iManning & Holthuis, 1984, by original designation). Chaceon manningi sp. nov. (Colour pl. 1, figs. 1-4) -- Material examined. Holotype male, cw 185 mm, cl 159 mm (ZRC 1993.6588), Tung-Sa Islands, South China Sea, 438-636 m depth, trawled by R/V "Hai-Kung", obtained by D.-A. Lee, l3.vi.1991. Paratype male, cw 187 mm, cl 167 mini (NTOU 1991-6-18), same data as holotype. - Description of holotype. A very large Chaceon, cw 185 mm, cl 159 mm, dorsal surface convex transversely and longitudinally. Gastric region swollen, strongly rugose and punctate but not granulose. Hepatic regions gently convex, slightly rugose, not granulose. Each branchial region with one distinct, trans- verse granulated ridge opposite fourth and fifth anterolateral teeth; with one weaker, less distinct, shorter ridge both anterior to, and posterior to main ridge; postero-branchial region swollen, strongly granulose and rugose. Suborbital, sub-branchial and subhepatic regions smooth; pterygostomial region rugose, punctate. Median frontal teeth slightly smaller and extending slightly forward of lateral frontal teeth, distance between median frontal teeth ca. 0.7 times distance between median and lateral frontal teeth. Supraorbital margin with a small submedian fissure and another adjacent to external edge; fissures not obvious from dorsal view. Infraorbital margin lined with small rounded gran- ules, inner edge with sharp, acutely triangular tooth. Anterolateral margin convex; first, third, and fifth anterolateral teeth small, low, triangular, not spiniform, second and fourth very low to almost obsolete. Posterolateral margin distinctly convex, rugose. Posterior margin of carapace subcristate, median margin distinctly concave. Cornea of eyes well-developed, pigmented. Anten- .