Nipponocercyon, Sato, 1963

Hoshina, Hideto & Fikáček, Martin, 2010, Morphological study and taxonomic revision of the genus Nipponocercyon (Coleoptera: Hydrophilidae: Sphaeridiinae), Acta Entomologica Musei Nationalis Pragae 50 (1), pp. 117-130 : 128

Recognition of Nipponocercyon and its position within Megasternini

The genus Nipponocercyon is well delimited from all other genera of the Megasternini and may be easily recognized by the combination of the following characters: i) presence of two short mesal ridges on the anteromedian part of the metaventrite (unique character), ii) antennae with groups of peg-like sensilla on ventral surface of antennomeres 7–8 (unique character), iii) presence of shallow depressions on the ventral surface of the profemora, iv) the shape of the median portion of the prosternum, v) antennal grooves not reaching the lateral margins of the hypomeron, and vi) abdominal ventrites 2–5 bare in contrast to ventrite 1. Characteristic is also the colouration of elytra, in which N. shibatai is only similar to Cercyon alinae Ryndevich, 2004 ; this character may help in routine identification.

FIKÁČEK (2007, 2010) discussed two broadly defined groups of megasternine genera. Nipponocercyon belongs neither to the ‘ Megasternum group of genera’ (based on the antennal grooves not reaching lateral margins of the hypomeron and the well-developed anepisternum 3) nor to the ‘Gondwanan group of genera’ (based on the morphology of the male genitalia: median lobe not attached to the base of parameres and freely movable inside of the phallobase, sternite 9 with a large median tongue-like projection and sternite 8 without a narrow anterior projection). The precise position of Nipponocercyon is at present unclear.

Besides the above characters, Nipponocercyon is very unusual in having very large mesothoracic cavities for the reception of the procoxae. The cavities reach the mesocoxae, which is otherwise known only in the genus Australocyon Hansen, 1990 . Nipponocercyon might be related especially to the A. pilocnemoides species group (sensu HANSEN 2003), which seems unrelated to other Australian or Neotropical species of Australocyon . There are also similarities with the Afrotropical genus Pseucyon d’Orchymont, 1948 (similar morphology of the preepisternal plate, pubescence and punctation of the abdominal ventrites and presence of a ridge delimiting the median portion of the prosternum from the lateral parts) and with the Oriental genus Gillisius d’Orchymont, 1925 (similar morphology of the preepisternal plate and presence of a ridge delimiting the median portion of prosternum from the lateral parts). However, both Pseucyon and Gillisius have much smaller mesothoracic cavities for the reception of the procoxae, i.e. not reaching the mesocoxae.