Additive typogenesis in Thoanteus (Gastropoda: Bulminidae)

Thoanteus ferrarii sp. nov. from Crimea is described. The phylogeny of Thoanteus is reconstructed in a cladistic analysis and the evolution of this genus is discussed. Thoanteus ferrarii sp. nov. represents an early stage in the additive typogenesis of Thoanteus , in which the appendix retractor still inserts laterally at the appendix section A₁, a short distance from its proximal top, as in the Peristoma-like stem species of Thoanteus.