ased on the results of an ecosystem survey carried out by the Murmansk Marine Biological Institute (MMBI) in the Laptev and East Siberian seas, the sponge fauna of the considered areas was studied. A total of 26 sponge species were identified. Some species were new records for the study area, i.e. Mycale helios, Tetilla sandalina, Halichondria sp., Polymastia rara, Lycopodina cupressiformis and Pseudosuberites montiniger. Three species were new to science, i.e. Suberites cebriones sp. nov., Artemisina lundbecki sp. nov. and Iophon koltuni sp. nov. In general, the inhospitable environment of the New Siberian shoal area is characterised by a predominance of boreal Arctic species in the faunistic composition, mostly of Atlantic origin. However, an overwhelming number of these species are regarded here as representatives of a proposed group of secondary Arctic species. Such species certainly originated from the North Atlantic fauna, but during the Pleistocene glaciation became isolated and continued to evolve independently. The phenomenon of ecological vicariance (which has repeatedly been observed for diverse groups of Arctic animals) is discussed here as a confirmation of the hypothesis.