Deep-sea acorn worms (Enteropneusta) from the Bering Sea with the description of a new genus and a new species of Torquaratoridae dominating soft-bottom communities

Five species of deep-sea acorn worms (Enteropneusta) were found in the Bering Sea during cruises of the RV Akademik M.A. Lavrentyev in 2016, 2018, and 2021. The worms were recorded on slopes of the Volcanologists Massif and in the Komandorsky Graben at depths between 1830 and 4278 m and on the Koryak slope between 419 and 662 m. Four of the species were only photographed but not collected; these were an unidentified Torquaratoridae gen. sp. 1 and three harrimaniids: Saxipendium sp., Harrimaniidae gen. sp. 1 and Harrimaniidae gen. sp. 2. Harrimaniidae gen. sp. 1 and gen. sp. 2 were recorded on the Koryak slope in the vicinity of methane seeps. The fifth species was photographed in situ and collected. It has been examined using morphological and molecular methods. It is described in the present study as Quatuoralisia malakhovi n. gen. n. sp. Ezhova et Lukinykh (fam. Torquaratoridae). The abundance of this species in the soft-sediment community at the depth 1830-2290 m was up to 12 specimens per m², the highest ever recorded for any deep-sea enteropneusts. Morphologically, Q. malakhovi n. gen. n. sp. is noteworthy for the mesocoel ducts, the heart-kidney complex with a pericardial coelom, the two-plated skeleton supporting the proboscis stalk, and conspicuously elongated lateral wings developed on either side of the trunk. The molecular analysis based on the mitochondrial 16S rRNA showed that Q. malakhovi n. gen. n. sp. is closest to several torquaratorid species that have yet to be formally described morphologically.