Morphological study and taxonomic revision of the genus Nipponocercyon (Coleoptera: Hydrophilidae: Sphaeridiinae)

Abstract: External morphology and male genitalia of the endemic Japanese genus Nipponocercyon Satô, 1963 are examined and the taxonomy of the genus revised based on specimens from nine localities at the islands of Kyushu, Shikoku and Honshu. All examined specimens are found to belong to the same species, N. shibatai Satô, 1963, which shows a considerable intraspecifi c geographic variability in the shape of the preepisternal elevation of the mesothorax, intersticial microsculpture of the mentum, pronotum and elytra and the morphology of the basal portion of the elytra. Two new synonyms of N. shibatai are proposed, N. shibatai oyamanum Nakane, 1968, syn. nov. and N. monticola Nakane, 1968, syn. nov. Important diagnostic characters of the genus as well as the intraspecific variability of the above characters are illustrated in line drawings and SEM photographs. Geographic patterns of the variability are discussed.

Key words: Megasternini, Nipponocercyon, morphology, taxonomy, intraspecific variability, synonymy, endemics, distribution, islands, Japan, Palaearctic Region