Anatomy and function of the penial twin papillae system of the Helicinae (Gastropoda: Helicoidea: Helicidae) and description of two new, small Hemicycla species from the laurel forest of the Canary Islands

Abstract

Hemicycla laurijona sp. nov. and H. fulgida sp. nov. are described from the laurel forests of La Gomera and Tenerife islands, respectively (Canary Islands). Both species belong to the Helicinae group of genera sharing the “presence of a specialized twin papillae system” in the penis, the adaptive advantage of which has not hitherto been discussed. Both species present a proximal penial papilla homologous to the “penial papilla” of other Stylommatophora, and an apomorphic distal penial papilla. The arrangement of these organs is described in a specimen with the distal genital system everted, showing that the distal penial papilla is an accessory papilla whose main function may be to lengthen the male duct in the evaginated penis. The accessory papilla may also have another function; its base forms a protuberant ring in the everted penis, perhaps for anchorage during mating or to impede a too deep penetration. The dart and an undigested part of the spermatophore of H. fulgida are also described, the species status of both H. invernicata (Mousson, 1872) and H. consobrina (A. Férussac, 1822) is confirmed and some aspects of Hemicycla relationships are discussed.