Comparative mitogenomic analysis reveals cryptic species in Reticunassa festiva (Neogastropoda: Nassariidae).

The mitochondrial genome provides sets of genome-level characteristics, which can be useful in resolving ancient relationships. The complete mitochondrial genomes of five Reticunassa and one Nassarius were sequenced, including Reticunassa hiradoensis, R. fratercula, R. festiva complex A, B and C and Nassarius variciferus, and compared with other two Nassariidae species (Tritia reticulatus and T. obsolete). Eight genomes show the same gene order as in other caenogastropods, containing 13 protein-coding genes, 2 ribosome RNA genes and 22 transfer RNA genes, except R. fratercula, which lacks the trnF. Three-nucleotide deletion in nad6 genes, truncated major non-coding regions are detected in all Reticunassa mitogenomes. The reconstructed phylogenetic trees show (Reticunassa + (Tritia + Nassarius)) at genus level and support the relationship between R. festiva-C and the clade formed by R. hiradoensis + R. fratercula and R. festiva-A + R. festiva-B within Reticunassa. The specific mitogenomic characters and phylogenetic analyses support the validity of genus Reticunassa. Pairwise genetic distances of protein-coding genes between R. festiva complex A, B and C range from 0.063 to 0.109, which are close to that of R. hiradoensis and R. fratercula (0.065), and higher than those of several closely related sister species of mollusks. These variation in mitochondrial genomes of Reticunassa indicate that R. festiva-A, R. festiva-B and R. festiva-C should be considered as separate species.