Integrative taxonomy reveals new taxa of Trochidae (Gastropoda: Vetigastropoda) from seamounts in the tropical western Pacific

Abstract

During two expeditions to seamounts near the Mariana Trench in the tropical western Pacific, several trochiform shells from the upper bathyal zone were sampled. Morphological observations of these specimens suggest that they represent two new species that belong to the family Trochidae, but the shell morphology, radular plan, and external anatomy differ considerably from those of closely related genera. A new subfamily, Carinotrochinae subfam. nov., and a new genus, Carinotrochus gen. nov., are proposed herein to accommodate these two species. Carinotrochus marianaensis sp. nov., the type species, was associated with coral debris at a depth of 865 m, and Carinotrochus williamsae sp. nov. was discovered crawling on a hydroid Stegolaria sp. that was attached to a dead bamboo coral at a depth of 1332 m. Genertic analysis of mitochondrial COI, 16S rRNA, and nuclear 28S rRNA genes using maximum likelihood, Bayesian inference, and pairwise uncorrected p-distances confirmed that the new taxa are trochids but do not belong to any existing defined subfamily. Molecular clock analysis based on concatenated sequences (COI, 16S, and 28S) indicated that Carinotrochinae subfam. nov. split from its shallow water sister subfamily Trochinae roughly 80 Mya during the Late Cretaceous.