Toxoglossan gastropods of the subfamily Crassispirinae (Turridae) lacking a radula, and a discussion of the status of the subfamily Zemaciinae

Two new species of Horaiclavus, lacking radula, venom gland and proboscis, are described. The genus is placed in the subfamily Crassispirinae (Turridae). Both species possess a peculiar foregut structure, the muscular rhynchodaeal outgrowth situated in the rhynchocoel. The possible function of the rhynchodaeal outgrowth is discussed. Other studied species of Horaiclavus possess a radula of a typical ‘crassispirine’ type but lack the outgrowth. The anatomy of the foregut of the new species is superficially similar to that of Zemacies excelsa (Turridae: Zemaciinae), which also possesses an additional structure of the rhynchocoel, namely the ‘pyriform gland’. Conchologically, there is no resemblance between Zemacies and Horaiclavus and it is concluded that similar foregut arrangement appeared independently in both lineages. A new monotypic subfamily Zemaciinae was erected mostly on the basis of the unique foregut arrangement of Zemacies excelsa. We express doubts concerning the importance of these characters in establishing a new taxon of subfamilial rank and therefore the validity of the subfamily Zemaciinae.