Diversity and molecular phylogeny of the Indo-West Pacific rock dwelling Smaragdinella snails (Cephalaspidea, Haminoeidae)

Smaragdinella A. Adams, 1848 is a genus of marine gastropods belonging to the family Haminoeidae (order Cephalaspidea), confined to tidal zones of the tropical and sub-tropical Indo-West Pacific region. These snails are of special evolutionary interest because they are the only lineage of Cephalaspidea adapted to living directly on hard substrates. However, with only three valid species and 17 nominal names currently recognized, the taxonomy of Haminoeidae is problematic. This study presents the first global phylogenetic analyses of Smaragdinella based on 84 specimens from across the geographic range of the genus using complete mitochondrial genomes and partial nuclear ribosomal complex data (18S rRNA + 28S rRNA). Maximum likelihood, Bayesian inference and species delimitation analyses using the Assemble Species by Automatic Partitioning (ASAP) method, were employed to estimate the number of candidate species and infer their relationships. In addition, morphological analysis of shells and anatomical structures was performed in targeted specimens using dissections and scanning electron microscopy. The results suggest the presence of 13 or 14 candidate species clustering in two main clades largely separated by geography: one comprising Pacific Ocean and Red Sea species, and another consisting of Indian Ocean species. These clades are defined by synapomorphic traits with specimens from the Indian and Pacific clades having unique features of the shell, digestive and reproductive systems.