Vol 51, No 5 (2025)

Calyptogena pacifica (Bivalvia: Vesicomyidae: Pliocardiinae) is an amphi-Pacific, bathyal, chemosymbiotic species living near cold methane seeps, hydrothermal vents, and cetacean carcasses. In the present study, the genetic diversity of C. pacifica on the scale of the entire geographic range of the species is addressed for the first time, using a sequence of the cytochrome c oxidase subunit I (COI) gene. The material includes both own data obtained during a study of bivalve mollusks from the Koryak slope and the Piip Volcano, Bering Sea, and information on COI sequences of bivalves from five East Pacific regions published in GenBank. A total of 12 haplotypes have been identified, of which two are from both the West Pacific (Bering Sea) and the East Pacific, one only from the West Pacific, and nine only from the East Pacific. The results of analysis of molecular variance have not revealed significant genetic differences both between the samples from the Koryak slope and the Piip Volcano and between the combined samples from the West and East Pacific. Both groups of haplotypes, identified by the phylogenetic analysis, are not associated with any geographical area. The obtained data suggests no significant genetic differentiation of C. pacifica populations from the Bering Sea and the East Pacific in COI despite the spatial isolation of the habitats suitable for this bivalve mollusk.