Euopisthobranch mollusks of the order Cephalaspidea (Gastropoda: Heterobranchia) of the Kuril-Kamchatka Trench and the adjacent Pacific abyssal plain with descriptions of three new species of the genus Spiraphiline (Philinidae)

Abstract

Our study focuses on the distribution and diversity of different cephalaspidean species collected from the Kuril-Kamchatka Trench (KKT) during the deep-sea expeditions KuramBioI (2012), SokhoBio (2015) and KuramBioII (2016). Our study recovered several undescribed taxa from different parts of the KKT and the adjacent abyssal plain, belonging to four families: Cylichnidae s. l., Scaphandridae, Aglajidae and Philinidae. The molecular phylogenetic and species delimitation analyses based on four gene markers (COI, 16S, H3, 28S) were conducted to determine species identity and phylogenetic relationships of several taxa. The morphological analysis included anatomical dissections and scanning electron microscopy. Herein, we focus on the family Philinidae as the most common cephalaspidean taxon in the sampling area but also provide general remarks on all the groups. All studied philinids from the KKT and adjacent abyssal plain belong to the genus Spiraphiline, which has been recorded from the northwestern Pacific for the first time. Three new species are described based on morphological and molecular data: Spiraphiline hadalis sp. nov., Spiraphiline kurilokamchatica sp. nov., both from the KKT, and Spiraphiline okhotensis sp. nov. from the western slope of the KKT and the Kuril Basin of the Sea of Okhotsk. The new subfamily Hermaniinae subfam. nov. with the genera Hermania and Spiniphiline is established; other philinid diversity is assigned to the subfamily Philininae. Preliminary data obtained for other families indicate a high cryptic diversity in the studied area, along with a very complex evolutionary history, especially in the families Aglajidae and Cylichnidae.