Unmasking Antarctic mollusc lineages: novel evidence from philinoid snails (Gastropoda: Cephalaspidea)

Since its introduction, the genus Philine has epitomized numerous mollusc snails with strong morphological convergence. Recently, a molecular analysis including a wide taxon sampling split this group into four non-sister families. Although they are especially diverse in cold and deep waters, no comprehensive studies are available for the Antarctic counterparts. Here, our morpho-anatomical and molecular data suggest major changes in the systematics of the group. From the eight known species, two are synonymized, Antarctophiline amoena with A. alata, and A. gouldi with A. gibba, and two are transferred to the genus Antarctophiline, namely A. apertissima comb.n. and A. falklandica comb.n. Two new species are described, A. easmithi sp.n. and A. amundseni sp.n. from different depths in the eastern Weddell Sea. The elusive P. antarctica from the Ross Sea was found in the Weddell Sea and Waegelea gen.n. is erected to place this species. Both phylogenetic and morphological data support the erection of Antarctophilinidae fam.n. to embrace most of the Philinoidea species described in the Southern Ocean. Only two species of Philinidae are found in Antarctic waters, Spiraphiline bathyalis gen. et sp.n. from bathyal depths in the Weddell Sea and S. kerguelensis comb.n. from the Kerguelen Islands. In light of the new data provided for all described species and the phylogenetic framework proposed herein, we briefly discuss the diversification and biogeographical patterns of Antarctic philinoid snails. Overall, antarctophilinid species seem to have restricted and grossly nonoverlapping distributions suggesting allopatric speciation connected possibly to geographical or bathymetric isolation.