Partial 28S rDNA Sequences and the Antiquity of Hydrothermal Vent Endemic Gastropods

A molecular phylogenetic investigation of the hypothesized antiquity of the hydrothermal vent endemic Neomphalina (Mollusca; Gastropoda) is reported. Sequences of two domains of the gene encoding for 28S ribosomal RNA were acquired for 3 outgroup and 32 gastropod genera. Use of the likelihood ratio test indicated complex substitution patterns for these domains and taxa, corresponding to a general time-reversible model with among-site rate variation. Phylogenetic analyses were performed using this model under maximum likelihood criteria. The data lacked resolution of gastropod radiations of the Paleozoic and all three of the outgroup sequences were randomized relative to the ingroup. Acceleration of evolutionary rates had additionally randomized the sequences of the Patellogastropoda relative to the other Gastropoda. The data resolved radiations of the Mesozoic and supported monophyly of the sampled Neritopsina, Vetigastropoda, Neomphalina, Caenogastropoda (including Campanile and the Architaenioglossa), and Heterobranchia (Valvata + Euthyneura), although several results were not significantly different from nonmonophyletic alternatives. Mesozoic origins of the hydrothermal vent endemic Neomphalina are preliminarily supported and implications for the hydrothermal vent refugia hypothesis discussed. Issues related to phylogenetic resolution of the Gastropoda are additionally discussed.