The results of an investigation into coelenteron content of the Antarctic sea anemone Urticinopsis antarctica Carlgren, 1927 are presented. Remains of invertebrate animals and fishes were found in the gastrovascular cavity of anemones. Some of them were damaged by digestion and were considered as food items of U. antarctica. These items were molluscs Addamussium colbecki (Smith, 1902), Laevilacunaria pumilia Smith, 1879, Eatoniella caliginosa Smith, 1875 and one not strictly identified gastropod species from the family Rissoidae; a crinoid from the family Comatulida; sea-urchin Sterechinus neumayeri Meissner, 1900; ophiuroid Ophiurolepis brevirima Mortensen, 1936 and a fish Trematomus sp. In contrast to the prey mentioned above, three specimens of amphipods Conicostoma sp. were not destroyed by digestion. They may represent commensals, which live in the gastrovascular cavity of the anemone.

The opinions of systematists about the classification and evolution of burrowing sea anemones have repeatedly changed over the long-term study of Actiniaria. Four stages can be distinguished over the course of the classification history. Each system was characterized by the use of mainly one particular feature. These features were: (1) characters of the external morphology, (2) arrangement of the mesenteries, (3) presence or absence of the basilar muscles and (4) molecular markers. The views on the origin and the evolution of the burrowing sea anemones were also altered more than once, that led to the emergence of several hypotheses. The burrowing sea anemones were considered as a primitive group or, on the contrary, as more advanced descendants of large hexamerous actinians.

Based on the study of new collection material and literature data, the composition of the sea anemone fauna of the Kara Sea is described. It includes 13 species of 7 families. Among them are 10 species that have previously been known for this region: Urticina crassicornis (O.F. Muller, 1776), Aulactinia stella (Verrill, 1864), Hormathia digitata (O.F. Muller, 1776), Allantactis parasitica Danielssen, 1890, Actinostola callosa (Verrill, 1882), A. spetsbergensis (Carlgren, 1893), Anthosactis janmayeni Danielssen, 1890, Halcampa arctica Carlgren, 1893, Edwardsia arctica Carlgren, 1921, Ptychodactis patula Appellof, 1893, and 3 species reported for the Kara Sea for the first time: Cactosoma abyssorum Danielssen, 1890, Haliactis arctica Carlgren, 1921, and Edwardsia vitrea Danielssen, 1890. The ranges of the species are described. A detailed consideration of the species’ geographical distribution, determined by the temperature, depth and salinity, allows the anemones to be subdivided into 3 groups: a) inhabiting the shelf and associated with high salinity; b) eurybathic, associated with the high latitudes, high salinity and a narrow interval of low temperatures; c) the most widespread, withstanding desalination and low temperatures. The geographic ranges of epibenthic polyps of the infraorder Thenaria have now been thoroughly studied, but the distribution of the representatives of the infraorder Athenaria in Arctic is known only from several finds. The distribution of the only Arctic representative of the suborder Ptychodacteae, Ptychodactis patula, is known from a fairly large number of finds, but its habitat requirements are little known. Therefore, our reasoning about the sources of the formation of the Kara Sea fauna is based mainly on the data derived from the thenarians. Our analysis has confirmed the participation of the species of Atlantic origin, most resistant to low temperatures, in the formation of the Kara Sea fauna, but no convincing evidence has been found for the participation of Pacific elements in the settlement of this region.

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