Ascetoaxinus ravichandrani sp. nov., a new species of deep-water Thyasiridae (Mollusca: Bivalvia) from the northern Indian Ocean

A new species of deep-sea thyasirid (Bivalvia: Thyasiridae), Ascetoaxinus ravichandrani sp. nov., is described and illustrated from material collected in the northern Indian Ocean during the FORV Sagar Sampada deep-sea cruise no. 404. Specimens were collected from a depth between 1007 m and 1038 m off Kanyakumari, Gulf of Mannar, Tamil Nadu, South India. This is the first record of the genus Ascetoaxinus from the Indo-West Pacific. The new species is compared to A. quatsinoensis P.G. Oliver & Frey, 2014 from the Northeast Pacific and A. ovoideus (Dall, 1890) from the Northwest Atlantic. It can be distinguished from these species by its external shell characters. Further comparisons are made between the new species and other larger thyasirids recorded from deep waters around India, notably Channelaxinus investigatoris E.A. Smith, 1895. The distinctions and similarities among these species are discussed, highlighting the key features that set A. ravichandrani apart from related species.