Leptochiton subrugatus sp. nov. (Mollusca: Polyplacophora) from low boreal waters of northern Pacific

Abstract: The genus Leptochiton Gray, 1847 is a paraphyletic group of small, pale, and usually deepwater chitons. They lack some of the morphological shell characters that are important in the systematics of Polyplacophora, and species identification within this genus is challenging. One species complex in the North Pacific includes at least 11 species that were historically synonymized or confused with Leptochiton rugatus (Carpenter in Pilsbry, 1892). Scrutiny of ecological and biogeographical patterns has helped to separate species lineages within this clade and support morphological diagnoses. Based on morphological and molecular studies, a new species is described that was previously confused with both Leptochiton assimilis (Thiele, 1909) and Leptochiton rugatus. This new species is widely distributed in the summer-warmed bays of the southern Primorye, Moneron Island, Northern Japan, Kunashir, and the Yellow Sea. This species is at least ~8% different in the COI barcode region from Leptochiton rugatus s.s. Morphological differences between the new species and closely related species are presented.