The relationships of the enigmatic gastropod Tritonoharpa (Neogastropoda): New data on early neogastropod evolution?

In this paper, the relationships of Tritonoharpa Dall, 1908, within Neogastropoda are discussed. Tritonoharpa is indeed similar to Colubraria in the morphology of its head-foot, pallial complex, reproductive and excretory systems, in the presence of an extremely long and coiled proboscis, and a very large stomach. However, it differs from Colubraria in the rest of its foregut anatomy, revealing a cancellariid affinity, and a typical nematoglossan radula. The molecular data confirms Beu and Maxwell's placement of Tritonoharpa in the Cancellariidae, close to Plesiotriton. It is also suggested that cancellariids may be the sister-group to the rest of neogastropods. Tritonoharpa has a rather large and well developed midgut gland, resembling the gland of Leiblein. As previously studied cancellarioideans have been shown to lack a well differentiated gland of Leiblein, the present study raises some interesting questions about the evolution of the foregut in Neogastropoda. In fact, if this glandular structure were confirmed as a true homologue of the gland of Leiblein, and the cancellarioideans proved to be the sister group to the remaining neogastropods, the possession of the gland should be considered a synapomorphy of the Neogastropoda.