Description of a new species of Somanniathelphusa (Decapoda, Brachyura, Parathelphusidae) from Vietnam

Ng & Kosuge (1995) recently described a new species of rice® eld crab, Somanniathelphusa pax, from specimens obtained from markets in Hanoi, Vietnam.

Subsequently, more lots of recently obtained crab specimens from markets in Hanoi were examined as part of the ® rst author’s revision of Indochinese freshwater crabs, resulting in the discovery of a second Somanniathelphusa species, apparently being sold in markets in heterogeneous lots together with S. pax.
This second species has proven to be new to science and is named herein as Somanniathelphusa dangi.

Four species of rice® eld crabs have previously been reported from northern Vietnam [formerly ª Tonkinº ], viz., Somanniathelphusa sinensis (H. Milne Edwards, 1853), S. kyphuensis Dang, 1975, S. pax Ng & Kosuge, 1995, and Esanthelphusa dugasti (Rathbun, 1902) [as Somanniathelphusa dugasti] (see Rathbun, 1905; Balss, 1914; Bott, 1968, 1970; Dang, 1975; Ng & Kosuge, 1995). Among these, the records of S. sinensis and E. dugasti are highly doubtful as they are only known to occur in south-western China and northeastern Thailand, respectively (Ng & Dudgeon, 1992; Ng & Kosuge, 1995). The records of S. sinensis from northern Vietnam are probably S. dangi sp. nov., S. kyphuensis or both, while those of E. dugasti from northern Vietnam are probably S. pax.

Naiyanetr (1994) split the genus Somanniathelphusa Bott, 1968, into four genera: Somanniathelphusa s. str.; Sayamia Naiyanetr, 1994; Esanthelphusa Naiyanetr, 1994; and Chulathelphusa Naiyanetr, 1994. However, forms with intermediate ® rst gonopods G1 and/or carapace characters have been found, indicating that a reappraisal of these groupings may be necessary, but this will not be discussed any further here as it is not within the scope of the present paper.

Somanniathelphusa dangi sp. nov. therefore, has been tentatively assigned to the genus Somanniathelphusa s. str. (sensu Naiyanetr, 1994) as the form of its G1 is closest to that of the type species, S. sinensis (H. Milne Edwards, 1853).

The present paper serves to describe Somanniathelphusa dangi sp. nov. The following abbreviations are used: G1 for male ® rst pleopod, G2 for male second pleopod. Measurements are of carapace width and length respectively. Terminology used essentially follows Ng (1988). All measurements are in millimetres. Specimens examined are from the Zoological Reference Collection (ZRC), Department of Biological Sciences, National University of Singapore, Republic of Singapore; Zoological Museum of Hanoi University (ZMHU), Vietnam; United States National Museum (USNM), Smithsonian Institution, Washington D.C., U.S.A.; MusÂeum National d’Histoire Naturelle (MNHN), Paris, France; and Senckenbergischen Naturforschenden Gesellschaft (SMF), Frankfurt, Germany.