Three predominant species groups of deep-sea whelks (Gastropoda: Buccinidae) in the Sea of Japan: their molecular taxonomy and geographic distribution

Abstract

Based on 3,484 specimens collected from a series of surveys, we revealed that three species groups of deep-sea whelks (Buccinidae) are distributed predominantly in the Sea of Japan (off Honshu Island, 200–1,900 m in depth). The first species group is composed of species of the genus Neptunea. Although N. intersculpta and N. constricta have been considered as representatives of the Sea of Japan, our mitochondrial (mt) 16SrDNA data showed no clear reason to recognize more than one taxonomic unit for them. The second is composed of Buccinum tsubai; three haplogroups off Honshu Island were reconfirmed using 16SrDNA sequences. The present study demonstrated two of these haplogroups distributed in the same region near the Noto Peninsula. The last group, made up of B. striatissimum and related taxa, is still problematic despite our present morphological and molecular analyses. In our tentative conclusion, two different species are widely distributed off Honshu Island, one is B. striatissimum inhabiting in shallower regions (< ca. 500 m in deep) and another is B. tenuissimum in deeper regions. To overcome the remaining uncertainty related to the genetic differentiation of these two species, further clarification of their taxonomic relationship is needed. Geographical distributions of these three species groups are detailed based on the present study.