Geographical and vertical distribution of Axinulus (Bivalvia: Thyasiridae): New data on distribution in the North Pacific and description of a new species

Abstract

The genus Axinulus is the richest in species number and quantitative abundance among representatives of the family Thyasiridae, which is found in the abyssal and hadal zones of the deep-sea areas of the northern Pacific Ocean. Many species of the genus form abundant populations and dominate the benthic communities of these deep-sea areas. The study of the material of bivalves collected by the “AleutBio” deep-sea expedition (2022) in the eastern part of the Aleutian Basin (Bering Sea) and in the Aleutian Trench revealed the occurrence of three species of the genus Axinulus, one of which turned out to be new to science, and Axinulus krylovae and Axinulus oliveri were first records for the eastern Pacific. Here, we describe Axinulus pentagonalis sp. nov. found in the Bering Sea and on the oceanic slopes of the Aleutian Islands at depths of 3646–4630 m and present new data on the distribution of A. krylovae and A. oliveri. The main feature distinguishing the new species from other species of Axinulus is the presence of a unique sculpture of the prodissoconch consisting of thin, curved, ramified, and branched folds extending from a short ridge in the middle of the prodissoconch. In addition, the new species differs from most of related species in the presence of a bulbous tip of the foot divided into two parts. We compare the new species with all related species and analyze the geographic and vertical distribution of all species of the genus Axinulus supplemented by new data.