The species of Mathildella Guinot and Richer de Forges, 1981 and Neopilumnoplax Serène in Guinot, 1969 (Decapoda: Brachyura: Mathildellidae)

Abstract

The mathildellid crab genus Neopilumnoplax Serène in Guinot, 1969 was originally proposed for several deep-sea species previously placed in Pilumnoplax Stimpson, 1858, including P. sinclairi Alcock and Anderson, 1899 from the Bay of Bengal. Further revision led to creation of Mathildella Guinot and Richer de Forges, 1981, which differed chiefly from Neopilumnoplax in having one instead of two pairs of endostomial ridges, and in the width of the anterior abdominal somites. Most species of both genera are relatively well known, but N. sinclairi, until now, was known with certainty only from the type description and figure of the female holotype housed in the collections of the Zoological Survey of India. Examination of the holotype of Pilumnoplax sinclairi, facilitated by the late Michael Türkay, revealed P. sinclairi to belong to Mathildella instead of Neopilumnoplax. Moreover, comparison of M. sinclairi with M. kyushupalauensis Takeda and Watabe, 2004 from Komahashi Seamount off Japan revealed that the two nominal species may well be synonyms. We defer synonymising the two species, however, until male M. sinclairi can be studied. We also clarify selected historical records of "Pilumnoplax" species from Indonesia and mainland Japan, from which we confirm the occurrence of Mathildella serrata (Sakai, 1974) and M. kyushupalauensis, respectively. In addition, we recognise an additional character separating Neopilumnoplax from Mathildella in the respective presence or absence of epibranchial ridges on the carapace. Neopilumnoplax michalis sp. nov. from the Southwest Indian Ocean Ridge is described and compared with its nearest congener, N. heterochir (Studer, 1883) from off southern Africa. The identity of Pseudorhombilia (Pilumnoplax) normani Miers in Tizzard, Moseley, Buchanan and Murray, 1885 from Nightingale Island (Tristan da Cunha) and Agulhas Bank, off South Africa, is fixed by lectotype designation as a junior synonym of N. heterochir.