How to achieve internal fertilization without a vagina: the study case of the genus Archilina Ax, 1959 (Platyhelminthes, Proseriata) from Canary Islands

Five new species of Monocelididae (Platyhelminthes, Proseriata) are described from Eastern Atlantic. Three new Archilina species came from the Canary Islands. Two of them have the cirrus provided with a stylet, cylindrical in Archilina regina sp. nov. and spike-like in Archilina imperatrix sp. nov. Both species lack a vaginal pore: ventrally to the bursa, an area of vacuolar parenchyma is present. Archilina coronata sp. nov. lacks a stylet and has a vaginal pore. The three species are sister taxa to Duploperaclistus circocirrus and Duplominona miranda sp. nov., from Brittany (France), characterized by an extremely long, tubular stylet, about 150 μm in length. A further Archilina is described from Cabo Verde Islands, Archilina regisfilia sp. nov., with a funnel-shaped cirrus and without a vaginal pore. The finding in the Canary Islands of closely related species, occurring abundantly in the same habitats and differing for presence/absence of stylet and vaginal pore, suggests a role of the stylet in allowing internal fertilization in species without external vagina. The phylogeny presented, based on rDNA 18S and 28S genes, does not reflect present systematics of the Monocelididae, and the monophyly of most genera is not supported.