Mitochondrial genomes of ellobioid gastropods: large-scale gene rearrangements and limitation in phylogenetic applications (Heterobranchia: Eupulmonata)

ABSTRACT Heterobranchia is a subclass of Gastropoda for which phylogenetic analyses based on mitochondrial gene sequences have not been entirely successful. Here, we report a complete mitochondrial genome of an ellobiid snail, Marinula pepita (Euthyneura: Eupulmonata: Ellobioidea), and its wholesale gene rearrangements from the presumed ancestral order for Heterobranchia. Our phylogenetic reconstruction based on this new genome and the available mitogenomic sequences recovered two sister clades in the superfamily Ellobioidea. Six genera with the ancestral gene order and short branches formed one of the clades (Trimusculus, Carychium, Ovatella, Ellobium, Leucophytia and Auriculastra). Four ellobiid genera with rearranged gene orders and long branches formed the other clade (Marinula, Pedipes, Melampus and Myosotella), regardless of their subfamilial assignments, thereby strongly questioning this topology [long branch attraction (LBA)]. A separate phylogenetic tree inferred from near-complete sequences of the nuclear 18S and 28S rRNA genes, on the other hand, was largely consistent with the conventional, morphology-based classification although suggesting the need of a new subfamily for Marinula. Mitochondrial sequences can be useful for inferring shallow divergences among certain ellobioid genera and species, provided that particular attention is paid to avoid LBA artefacts.