Incorporation of microgastropoda species provides novel insights into phylogeny of Trochoidea (Gastropoda: Vetigastropoda).

Trochoidea is the richest and most diverse group within Vetigastropoda, serving as one of the main focuses on studies of marine ecology and systematics. Both morphological and molecular studies have sought to resolve the phylogenetic framework of Trochoidea; however, the phylogenetic relationships among some lineages remain controversial. In order to explore the phylogenetic relationships within Trochoidea, we sequenced the mitochondrial genomes of 9 trochoids and analyzed them with data from 38 previously published mitochondrial genomes and 27 transcriptomic data representing 11 families within this group. The mitochondrial genomes of all Trochidae exhibited a consistent gene arrangement and showed conserved genome size and nucleotide composition; however, Colloniidae and Phasianellidae showed higher levels of gene order rearrangement. Furthermore, three-nucleotide insertions were observed in the cox1 gene of Colloniidae and nad4L gene of Phasianellidae, while three-nucleotide deletions were detected in nad4 gene of Trochidae. Both maximum likelihood and Bayesian inference analyses supported the monophyly of all families within the Trochoidea, except Tegulidae, and placed Liotiidae as sister to the rest of Trochoidea with poor to moderate support. Areneidae was recovered as the sister group to a clade including Phasianellidae and Colloniidae. These findings challenge the traditional classification of this family based on both morphological and molecular data. Our study provides new insights into the phylogeny of Trochoidea, especially with the incorporation of micromolluscs taxa, and highlight the significance of incorporating microgastropoda taxa into molecular phylogenetic reconstructions of gastropod subgroups.