Meeting Abstract
The phylogenetic relationships among certain groups of gastropods have remained unresolved, especially in the diverse subclass Opishobranchia. There is a total of seventy mitochondrial genomes for gastropods published on GenBank, but the opisthobranch order Nudibranchia is not well represented. The mitochondrial genomes of the nudibranchs Melibe leonina and Tritonia diomedea have been sequenced as part of this study and both coded for the typical thirteen protein-coding genes, twenty two transfer RNAs, and two ribosomal RNAs seen in other species. M. leonina lacked a twelve-nucleotide deletion in the cytochrome oxidase 1 gene that is present in four other species of Melibe. For phylogenetic analysis, the thirteen protein-coding genes from the mitochondrial genomes of all gastropods, obtained from NCBI, were combined into a single data set. Two separate phylogenetic analyses were performed: one of the class Gastropoda and one of the subclass Opisthobranchia. Both Bayesian and maximum likelihood analyses resulted in similar tree topologies. In the Opisthobranchia, five distinct orders were distinguished as monophyletic (Anaspidea, Cephalaspidea, Notaspidea, Nudibranchia, Sacoglossa). In the Gastropoda, two of the three traditional subclasses, Opisthobranchia and Pulmonata, were seen as paraphyletic groups, whereas Prosobranchia was monophyletic. In contrast, the four more recently named gastropod clades – Vetigastropoda, Neritopsina, Caenogastropoda, and Heterobranchia – were all monophyletic, and thus appear to be better classifications for this diverse group.
