Aspects of the anatomy of Plesiotrochus (Plesiotrochidae, fam. n.) and its systematic position in Cerithioidea (Prosobranchia, Caenogastropoda)

Abstract

Anatomical features of species in the genus Plesiotrochus Fischer, 1878, support its allocation to the superfamily Cerithioidea Ferussac, 1819. Plesiotrochus has many apomorphic characters incompatable with those of any other known cerithioidean family. Accordingly, Plesiotrochus species are referred to Plesiotrochidae, fam. n., which is distinguished among cerithoideans by 7 autapomorphic characters. The genera Hemicerithium Cossmann, 1893, and Hypotrochus Cotton, 1932 are here considered to be synonymous with Plesiotrochus. Plesiotrochus was historically considered as a subgenus of Trochocerithium Cossmann and Sacco, 1896, but the latter genus is a turritellid, and is excluded from Plesiotrochidae. Plesiotrochus Fischer, 1878, an obscure cerithioidean genus, is rarely mentioned in the literature and has never been reviewed comprehensively. A cursory literature search indicates that it is not a large group, comprising approximately 11 nominal species. Aside from the radula and operculum of Plesiotrochus monachus (Crosse and Fischer, 1864) illustrated by Hedley (1907, pl. 17, figure 17), no anatomical information about any species in the genus exists.