Permian (Capitanian) gastropods from the Akasaka Limestone (Gifu Prefecture, Japan)

Abstract

A gastropod fauna from the Permian (Capitanian) Akasaka Limestone from Japan is described. It is one of the most diverse known Permian gastropod faunas and consists of at least 74 species level taxa. Forty taxa have been identified to species level; the remainder are treated in open nomenclature because of insufficient preservation. In addition, three types of neritimorph opercula are present. One family, seven genera and 28 species are described as new by Nützel. New taxa are the family Araeonematidae, the genera Coeloconulus, Asamiella, Costataenia, Akasakiella, Cerithiozone, Yochelsonistylus and Permocerithium, and the species Anomphalus japonicus, Anematina parva, Araeonema panthalassica, Coeloconulus panae, Trochonodus permianus, Goniasma fortecarinata, G.? nodifera, Vebericochlis mazaevi, Costataenia hayasakai, Trypanocochlea parva, Cerithiozone ornata, Cerithioides angulatum, Stegocoelia akasakaensis, Yochelsonistylus seussae, Y. felixi, Knightella hydrobiformis, Palaeostylus? irregularis, P. attenuatus, P. minutus, P. lateapicatus, Permocerithium nudum, Protorcula permiana, Medfrazyga convexa, M. rectecostata, Acteonina koizumii, Heterosubulites fusiformis, Nanochilina japonica and Streptacis orientalis. The gastropod fauna of the Akasaka Limestone has previously been known for containing some of the largest species from the Permian and the entire Palaeozoic, with specimens as large as 40 cm. The fauna is strongly dominated by molluscs and especially by gastropods and bivalves. The dominance of these groups represents a modern aspect of this fauna. Among the gastropods, high-spired caenogastropods form the most diverse and abundant group. Most of the new gastropod genera are related to Cerithioidea and some have anterior siphonal canals. This suggests an early radiation of these caenogastropods in the Asia/Panthalassa realm. The relatively large number of new taxa suggests that gastropod faunas of this region have been poorly sampled or preservation of such faunas is only sporadic. Several of the present genera and a few species are also known from Permian deposits in China, Malaysia, and Vietnam. Some of the genera are cosmopolitan.