The morphology and independent origin of ovoviviparity in Tiphobia and Lavigeria (Caenogastropoda: Cerithioidea: Paludomidae) from Lake Tanganyika

To better understand the diversification of the endemic thalassoid (i.e. marine-like) cerithioidean gastropods of Lake Tanganyika, as well as the origin and significance of brooding among lake species, we here redescribe the anatomy and ontogeny of the ovoviviparous Tiphobia horei from Lake Tanganyika and compare it to that of Lavigeria sp. A, representing another ovoviviparous lake clade that has acquired a uterine brood pouch independently. Within the phylogenetic framework provided by recent molecular analyses, the distant relation of these two taxa is corroborated by many external and internal anatomical differences. Comparison of the brood pouches demonstrates that they each bear unique features consistent with their independent modification for brooding. Despite representing functionally analogous structures, they also share several similarities in organization likely representing symplesiomorphies of the Lake Tanganyika species flock. The ontogeny is characterized by the presence of a velum and by delayed calcification producing a characteristically wrinkled embryonic cap. Comparison with other brooding cerithioideans reveals that T. horei and Lavigeria sp. A retain many more embryos than other freshwater cerithioideans of comparable size with a uterine brood pouch, possibly facilitated by the presence of longitudinal lamellae. Compartmentalization of the oviduct and delayed calcification is strongly linked to the brooding of embryos.