First record of an abyssal and hadal bryozoan fauna from the Kuril-Kamchatka Trench

Abstract

Abstract Benthic samples collected during cruise SO250 of the RV Sonne along the Kuril-Kamchatka Trench from three abyssal stations, at depths of 5134–5478\u202fm, and one hadal station, at depths of 7241–7245\u202fm, yielded one ctenostome and three cheilostome bryozoan species. The species encountered represent the deepest records of each genus. The record of Aethozoon pellucidum is the first hadal and the deepest for any species in the order Ctenostomata, increasing the number of known hadal bryozoan species to five. Our records of Aethozoon pellucidum and Atlantisina pacifica sp. nov. are the first for these genera in the Pacific Ocean, and that of Smithsonius quadratus sp. nov. is the first record for the northwestern Pacific. Bathymetrically, the fauna is equally represented by widespread eurybathic and abyssal stenobathic elements. Colony morphology is atypically diverse for the deep-water environment and includes four different forms, with A. pellucidum and Kinetoskias mitsukuri living on soft bottoms, and A. pacifica and S. quadratus colonizing hard substrata. No species was found on biotic substrata. The low degree of biomineralization of zooids in K. mitsukuri and A. pacifica coupled with their large size may reflect the synergistic effects of the deep-sea phenomena ‘rachitism’ and ‘gigantism’.