BIOGEOGRAPHIC AND PHYLOGENETIC AFFINITIES OF NORTH PACIFIC CALLIOSTOMATIDAE (VETIGASTROPODA)

Calliostomatidae Thiele, 1924 is a marine vetigastropod family distributed worldwide from the low intertidal to much deeper depths, mostly on rocky substrates but sometimes in sandy or kelp habitats. Many species have been placed by default in the oldest named genus, Calliostoma Swainson, 1840, resulting in its paraphyly. However, little is known about its phylogenetic relationships, especially within the North Pacific (NP), one of the most species-rich biogeographic regions. By focusing on the northeastern Pacific Calliostoma, we aim to resolve biogeographic patterns and phylogenetic relationships, specifically for the North Pacific Calliostomatinae. Results from our combined mitochondrial (COI + 16S) and non-coding nuclear region (internal transcribed spacer 2; ITS2) analysis, with greater taxon and gene sampling, extends the conclusions of previous studies. We find high support for a monophyletic NP Calliostomatinae clade with two main lineages: a NEP and a mixed NEP + NWP. The habitat usage for the NP parallels this phylogenetic split. Our results support a division of NEP species into separate radiations. One is endemic to the NEP and includes most familiar shallow-water species, while the other includes a mixture of NEP and NWP species and includes more deep-water species. Addition of the ITS2 region to our combined result improved the support for deeper affinities within the NP. As discussed by others, we also support the restriction of Calliostoma to the relatively few mostly European species most closely related to the type species C. conulus (Linnaeus, 1758). For desire of monophyly in the NP, we suggest that future revisions should use only Tristichotrochus Ikebe, 1942 and Otukaia Ikebe, 1942 for a mixed NEP + NWP lineage, and the remaining species that are resolved as a separate endemic NEP lineage should be placed in a newly described genus.