Adaptive evolution and phylogeny of cerithioid gastropods with six new mitogenomes.

Cerithioidea (Caenogastropoda: Gastropoda) represents a diverse superfamily of gastropods that inhabit marine, brackish, and freshwater environments worldwide. Despite this broad ecological distribution, their evolutionary history and phylogenetic relationships remain incompletely understood. Here, we report six newly sequenced mitochondrial genomes-two from Batillaria (Batillariidae) and four from Cerithidea, Cerithideopsis, and Pirenella (Potamididae)-to clarify cerithioidean phylogeny and investigate signals of adaptive evolution. Phylogenetic analyses consistently supported the monophyly of Cerithioidea and its subdivision into two major lineages. However, family-level relationships remained partially ambiguous. Batillariidae clustered with Pachychilidae, and Potamididae appeared as sister to Semisulcospiridae in most trees, underscoring the need for broader taxonomic sampling to refine these evolutionary relationships. Divergence-time estimates indicate that major lineages originated during periods of elevated global temperatures, with diversification accelerated by subsequent environmental changes, highlighting the influence of historical climate events on expansion and habitat shifts. Selection analyses reveal ND6 as a hotspot of positive selection, particularly within disordered protein regions that may enhance flexibility under environmental stress. These findings underscore how historical climate events and habitat fluctuations have influenced mitochondrial genome evolution in euryhaline gastropods, offering a refined phylogenetic framework for Cerithioidea and providing insights into the adaptive mechanisms underlying their expansive ecological range.