GUINOTHUSA, A NEW OF INDOCHINESE FRESHWATER (, GECARCINUCIDAE)

BY

DARRENC.J.YEO1,2) and PETER K. L. NG1,3) 1) Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Republic of Singapore

ABSTRACT

A new genus, Guinothusa, is established for three gecarcinucid species previously placed in Heterothelphusa Ng & Lim, 1986: Guinothusa beauvoisi (Rathbun, 1902), G. harmandi (Rathbun, 1902), and G. phimaiensis sp. nov. These species, from eastern Thailand and southern Vietnam, share a distinctive suite of diagnostic carapace, male abdomen, and G1 characters that distinguish them from the remaining species of Heterothelphusa,whichare known from the area along the Thai-Malaysian border. Guinothusa phimaiensis was previously a nomen nudum and a junior synonym of G. beauvoisi, and the name was never validated. A key to the species of Guinothusa is included.

RÉSUMÉ

Le nouveau genre Guinothusa est établi pour trois espèces de crabes d’eau douce gecarcinu- cidés classés auparavent dans Heterothelphusa Ng & Lim, 1986 : Guinothusa beauvoisi (Rath- bun, 1902), G. harmandi (Rathbun, 1902), and G. phimaiensis sp. nov. Ces espèces, de l’est Thailand et du sud Vietnam, partagent un ensemble de caractères sur la carapace, l’abdomen male et le G1, qui les séparent des espèces restantes d’Heterothelphusa connues des abords de la frontière Thailande-Malaisie. Guinothusa phimaiensis était un nomen nudum mais, comme il était considéré comme un junior synonyme de G. beauvoisi, ce nom ne fut jamais validé. Une clef des espèces de Guinothusa est présentée.

INTRODUCTION The gecarcinucid freshwater crab genus Heterothelphusa Ng & Lim, 1986, was originally established for one species, H. insolita Ng & Lim, 1986, from northern Peninsular Malaysia. Ng & Naiyanetr (1993) subsequently trans-

2) Corresponding author; e-mail: [email protected] 3) e-mail: [email protected]

© Koninklijke Brill NV, Leiden, 2010 Studies on Brachyura: 353-366 354 CRM 011 – Castro et al. (eds.), BRACHYURA: A HOMAGE TO DANIÈLE GUINOT ferred Potamon (Parathelphusa) beauvoisi Rathbun, 1902 [“Cochinchine” (= southern Vietnam)], to the genus, with Ng (1997) describing a third species, H. fatum Ng, 1997, from southern Thailand. Two other taxa, Pota- mon (Parathelphusa) harmandi Rathbun, 1902 [“Cochinchine” (= southern Vietnam)], and “Siamthelphusa phimaiensis Naiyanetr, 1978” nomen nudum [eastern Thailand], were regarded as junior subjective synonyms of H. beau- voisi (see Ng, 1988; Naiyanetr & Ng, 1990; Ng & Naiyanetr, 1993, 1997). Ng et al. (2008) recognized H. harmandi as a valid species of Heterothelphusa but without discussion. In recent years, we have had the chance to re-examine and compare all the extant material of species that have been referred to Heterothelphusa.The present study confirms that P. (P. ) harmandi and “Siamthelphusa phimaiensis” are in fact distinct species. These two taxa, together with H. beauvoisi, form a distinct morphological and geographical grouping, separate from the remaining Heterothelphusa species. We believe that these differences are of generic significance, warranting the establishment of a separate genus for these three species. A new genus, Guinothusa, is consequently established herein for H. beau- voisi, H. harmandi, and the revalidated “Siamthelphusa phimaiensis”, now for- mally named as Guinothusa phimaiensis sp. nov. Heterothelphusa is restricted to H. fatum and H. insolita. The following abbreviations are used: G1 for male first pleopod, G2 for male second pleopod. Measurements are of carapace width and length, respectively. The terminology used essentially follows Ng (1988). All measurements are in millimetres. The classification follows that proposed in Ng et al. (2008), with the difference being that Gecarcinucidae Rathbun, 1904, is now regarded as a senior subjective synonym of Parathelphusidae Alcock, 1910 (cf. Klaus et al., 2009). Specimens are deposited in the Muséum national d’Histoire naturelle, Paris (MNHN); National Museum of Natural History, Smithsonian Institution, Washington, D.C. (USNM); and the Zoological Reference Collection (ZRC) of the Raffles Museum of Biodiversity Research, National University of Singapore.

TAXONOMY

GECARCINUCIDAE Rathbun, 1904 Guinothusa gen. nov. Type species. — Guinothusa phimaiensis sp. nov., by present designation.