Unexpected biodiversity of epizoic gastropod genus Marseniopsis (Velutinidae) within a phylogenetic framework for the family

Marseniopsis Bergh, 1886 is a genus of marine gastropods (Velutinidae) which includes nine described species, eight of which endemic to Antarctica. This genus is characterized by a peculiar planktotrophic larva, the “limacosphaera”, with a potentially long pelagic life, which is a really uncommon developmental strategy for Antarctic gastropods. In addition, we observed several different colour patterns, within and amongst presumed conspecific samples. We produced a dataset of COI, 16S and 28S genes of 107 samples of Marseniopsis from the Ross Sea, the Dumont d'Urville Sea, the tip of the Antarctic Peninsula and the Weddell sector. Through genetic distances and Automatic Barcode Gap Discovery (ABGD) we identified 14 MOTUs, 10 of which exclusively from the Weddell Sea-Antarctic Peninsula. The isolation-by-distance analysis did not show any significant correlation between genetic and geographic distances among populations of each clade. These results suggest the presence of a hidden biodiversity of Antarctic Marseniopsis. Mantel colour turned out not to be a diagnostic character and probably due to the alimentary homochromy of Marseniopsis with ascidians. The absence of isolation-by-distance and the presence of some MOTUs in all sampling areas are congruent with the long pelagic life of the Marseniopsis larva. However, some MOTUs distribution restricted to Weddell Sea-Antarctic Peninsula lets hypothesize the existence of a second type of larva, with a limited dispersion capacity. We also produce a preliminary phylogenetic reconstruction of this family, as a starting point to extend our investigation to the Velutinidae worldwide.