Three new deep-sea species of Thyasiridae (Mollusca: Bivalvia) from the northwestern Pacific Ocean

Abstract

The Thyasiridae is one of the species-richest families in the abyssal and hadal zones of the northwestern Pacific Ocean. Many thyasirid species dominate benthic communities in terms of abundance and play an important role in the functioning of deep-sea ecosystems. Most of the thyasirid species in the region are new to science and have not been described. Based on the material collected from 1954 to 2016 by seven deep-sea expeditions, three new species of Thyasiridae (Parathyasira coani sp. nov., P. pauli sp. nov., and Thyasira kharkovensis sp. nov.) are described from the abyssal and hadal zones (3210–7540 m depth) of the Sea of Okhotsk, the Bering Sea, as well as the Kuril-Kamchatka and Japan trenches. The new species are remarkable among their congeners due to the combination of the following characters: an obliquely-rhomboidal shell with a weak and shallow posterior sulcus and a large prodissoconch with sculpture of lamellated folds. Comparisons with related species are provided.

Reduced chemosymbiont genome in the methane seep thyasirid and the cooperated metabolisms in the holobiont under anaerobic sediment

“…The ctenidium was large and thick, consisting of two demibranchs with numerous tightly spaced filaments. These morphological and anatomical features are consistent with the diagnosis of the genus Thyasira (Kamenev, 2023; Oliver & Holmes, 2006; Oliver & Killeen, 2002), and thus the studied thyasirid was identified as Thyasira sp. Unfortunately, the fragile shells of the collected specimen were damaged, which prevented their identification at the species level.…”

Three new species of Axinulus (Bivalvia: Thyasiridae) from the Japan and Kuril-Kamchatka trenches and abyssal zone of the northern Pacific Ocean

“…Remarks: Axinulus alatus sp. nov. has a wide range in the northern Pacific Ocean and was found off the Asian and American continents in the lower abyssal zone in the depth range of 3,000–5,000 m. The species was not found among extensive material of bivalves collected by the numerous deep-sea expeditions at depths greater than 5,000 m at the abyssal plain adjacent to the Kuril-Kamchatka and Japan trenches ( Okutani, 1974 , 2000 ; Okutani & Fujikura, 2002 ; Okutani & Kawamura, 2002 ; Kamenev, 2015 , 2018a ), as well as in the hadal zone of the Aleutian, Kuril-Kamchatka, and Japan trenches ( Okutani, 1974 , 2003 ; Okutani, Fujikura & Kojima, 1999 ; Fujikura et al, 1999 , 2002 ; Okutani & Fujiwara, 2005 ; Kamenev, 2019 , 2020 , 2023 ). In addition, this species was not recorded for the benthic fauna of the Kuril Basin (the Sea of Okhotsk) a little less than 3,300 m deep ( Kamenev, 2018a ), though it was found on the oceanic slope of the Kuril Islands opposite the deepest Bussol Strait connecting the Sea of Okhotsk and the Pacific Ocean.…”

“…71, July 6–August 6, 2015) in the abyssal zone of the Pacific slope of the Kuril Islands. The new species of Axinulus were found among the 72 samples of benthic fauna at depths of 3,200–9,583 m. The methods for the sample collecting and fixing have been in detail described previosly ( Monin, 1983 ; Brandt & Malyutina, 2015 ; Malyutina, Chernyshev & Brandt, 2018 ; Brandt et al, 2020 ; Kamenev, 2020 , 2023 ). The samples obtained during the expeditions of the IO RAS were stored in the IO RAS Ocean Benthic Fauna collection.…”

“…The methods for the sample preparation and the shell morphology study using the scanning microscopy as well as the gross anatomy analysis of the preserved alive-taken specimens have been described by Kamenev (2020 , 2023) . The microscopic studies of the new species described here were carried out at the Far Eastern Center of Electron Microscopy of the NSCMB FEB RAS.…”

“…Several years ago, the author of this article started a study of unidentified deep-sea species of the Thyasiridae found in the northwestern Pacific Ocean. As a result of this work, six new species have been described from the abyssal and hadal zones of the Sea of Okhotsk and the Bering Sea, the Kuril-Kamchatka and Japan trenches, as well as the oceanic plain adjacent to these trenches ( Kamenev, 2020 , 2023 ). The present article is a continuation of the study of northwestern Pacific deep-sea thyasirids and presents a description of three new species of the genus Axinulus that were found in the Japan and Kuril-Kamchatka trenches, as well as in the abyssal zone of other deep-sea regions of the northern Pacific Ocean.…”