The abyssal seafloor is an extreme environment, where organisms have to cope with high pressures, low oxygen and nutrient levels, permanent darkness, and low temperatures (with islands of extremely high temperatures around hydrothermal vents). Despite these obstacles, these deep-sea environments are home to a surprising range of organisms, including a number of Fungi which specialize in the decomposition of wood, a material of terrestrial origin. Do date only six species of obligate deepsea Fungi (i.e. Fungi found only in deep-sea environments) have been described, Alisea longicolla, Allescheriella bathygena, Bathyascus vermisporus, Oceanitis scuticella, Periconia abyssa, and Abyssomyces hydrozoicus, of which all except Abyssomyces hydrozoicus are wood-digesting species.
In a paper published in the journal Phytotaxa on 27 August 2024, Yukiro Nagano of the Marine Biodiversity and Environmental Assessment Research Center of the Japan Agency for Marine-Earth Science and Technology, and the Advanced Institute for Marine Ecosystem Change, Mohamed Adbul-Wahab of the Department of Botany and Microbiology at Sohag University, Ryota Nakajima, also of the Marine Biodiversity and Environmental Assessment Research Center of the Japan Agency for Marine-Earth Science and Technology, and Akinori Yabuki, also of the Advanced Institute for Marine Ecosystem Change, describe a new species of deep-sea wood-digesting Fungus from the Northwest Pacific abyssal plain.
The new species is placed in the genus Oceanitis on the basis of a genetic analysis, and given the specific name abyssalis in reference to the environment in which it was found, the abyssal plain of the Northwest Pacific close to the Kuroshio Extension current boundary. The species is described on the basis of a colony found growing on a branch of wood with bark still attached, from a depth of 5707 m.
Oceanitis abyssalis produces fleshy yellowish or brownish ascomycota (spore-producing bodies) on the surface of the wood, which are yellowish in colour, 1.2-1.6 mm high and 0.98-1.2 mm in diameter. It is very similar, both morphologically and genetically, to samples of Oceanitis scuticella collected from the Kuril-Kamchatka Trench, but is morphologically different from the original description of Oceanitis scuticella, which was based upon material from bathyal depths near the islands of Vanuatu, which was not genetically analysed, and is no longer available (to date, no deep-sea Fungus has been cultured in the lab). For this reason, Nagano et al. question whether the Kuril-Kamchatka Trench Oceanitis scuticella material should be placed in this species, suggesting that Oceanitis cf abyssalis might be a better designation for the time being.
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