Increased microgastropoda sampling give new insights into the phylogenetic relationships of Littorinoidea (Littorinimorpha)

Littorinoidea is one of the most diverse radiations and the most successful group that evolutionary transitions from marine to terrestrial within Littorinimorpha. With such an unmatched diversity, few phylogenetic investigations have attempted to understand their evolutionary relationships, and existing research has primarily focused on typical intertidal species. To address this gap, we conducted the first phylogenomic analysis of the Littorinoidea, leveraging 35 transcriptomes to investigate their internal relationships. Our analyses revealed significant revisions necessary within the Littorinoidea: 1) Pomatias appears distantly related to Littorinidae, suggesting a potential ancestral origin outside of Littorinoidea, challenging traditional classification. The homology of penial innervation within Littorinoidea warrants reevaluation. 2) Lacuna’s placement indicates a close relationship with Naticidae, prompting consideration for its removal from Littorinidae. 3) Based on the current phylogenetic research, Peasiella may belong to a distinct family separate from Littorinidae. 4) Our findings support revising the placement of Pteropods within the Littorinimorpha, which is situated phylogenetically between the families Littorinoidea and Naticoidea. Additionally, we highlight the impact of site heterogeneity and evolutionary rate variation on phylogenetic inference. Our study provides a robust phylogenomic framework for the Littorinoidea, emphasizing the importance of including microgastropoda taxa in molecular phylogenetic reconstructions of gastropod subgroups.