On the taxonomy of two rare freshwater crabs (Decapoda, Brachyura, Chasmocarcinidae and Hymenosomatidae) from Palau, western Pacific

Abstract

Abstract The taxonomy of two species of secondary freshwater crabs endemic to Palau is discussed. Males of the chasmocarcinid Australocarcinus palauensis Davie & Guinot, 1996 (Trogloplacinae), previously known only from one female, are reported for the first time and the species is redescribed and figured. This species is closest to A. kanaka Davie & Guinot, 1996, from New Caledonia, but can be distinguished by the form of the carapace, third maxillipeds and gonopods. The rare hymenosomatid Neorhynchoplax inermis (Takeda & Miyake, 1971) (Hymenosomatinae), known only from the original description, is here shown to be distinct from species of Neorhynchoplax Sakai, 1938 s. str., differing in its complete absence of a true rostrum, absence of postocular lobes, the relatively short ischia and meri of the third maxillipeds, unarmed ambulatory dactyli and strongly twisted male first gonopod. The species is redescribed and transferred to a new genus, Insulaplax.