Phylogenetic position of the deep-sea snail family Haloceratidae and new insights into caenogastropod relationships.

The phylogenetic position of Haloceratidae, a little-known family of the subclass Caenogastropoda, is contested due to its extreme rarity in bathyal waters worldwide (c. 800–3,500 m deep). Haloceratids share several morphological and ecological traits with members of Vanikoroidea, Tonnoidea, Capuloidea and Velutinoidea, and were provisionally included in Vanikoroidea based on the absence of certain apomorphic features of the latter three taxa. Here, we first investigate the phylogenetic position of the family based on molecular data from both of the recognized genera, Haloceras and Zygoceras. Reconstruction based on three nuclear and three mitochondrial gene sequences suggests that the Haloceratidae constitute a sister clade to the Capulidae and that the two families collectively form the superfamily Capuloidea. This superfamily is united in a large, robust clade with Calyptraeoidea, Velutinoidea, Tonnoidea and Neogastropoda. The superfamily Cypraeoidea, as previously conceived, was found to be polyphyletic; we propose new concepts of Cypraeoidea (including Cypraeidae and Ovulidae) and Velutinoidea (including Velutinidae, Eratoidae and Triviidae). This topology also confirms the polyphyly of taxa with the 'echinospira' type of larvae (Echinospirida). The morphological resemblance of these polyphyletic taxa highlights parallel acquisition of traits in response to the same selective pressures. [ABSTRACT FROM AUTHOR]