128 BIOLOGY OF THE SEAS OF THE U.S.S.R. 



The most characteristic molluscs are Joldia hyperborea, Cardium groen- 

 landicum, C. ciliatum, Nucula tenuis, Axinus flexuosus, Leda pemula, Mya 

 truncata, Macoma calcarea. Diastylis rathkei and amphipod Byblis gaimardi 

 are very numerous here. 



The fauna of the sublittoral sandy silt and of the pseudo-abyssal, middle 

 and great depths (60 to 360 m) is especially rich. The bottom fauna of the 

 so-called' trawling hole ' with its typical Forsimmitera. Hyperammina subnodosa, 

 polychaetes Onuphis conchylega, Nicomache lumbricalis, Maldane sarsi, 

 Pectinaria hyperborea, Polycirrus albicans, Gephyrea Phascolium strombi, 

 bryozoans Defrancia lucernaria, Alcyonidium gelatinosum, echinoderms 

 Ctenodiscus crispatus, Asterias lincki, Ophiura sarsi, crustaceans Calathura 

 carinata, has been thoroughly studied. Among the molluscs Astarte crenata 

 and Area glacialis are found here in large numbers. 



At the greatest depths, down to 400 m (pseudo-abyssal), certain Porifera 

 are added to this community, as for instance Myxilla brunnea, brachiopods 

 Terebratulina and Rhynchonella, the deep-sea echinoderm Rhegaster tumidus, 

 the crustacean Pontophilus norvegicus, and the molluscs Buccinum hydrophanum 

 and Pecten groenlandicus. 



There is an extremely original and rich life in the facies of the branched 

 Lithothamnion (calcareous algae of the Rhodophyta) forming abundant 

 clusters at places of strong water-circulation at depths of 10 to 40 m. Owing 

 to the large number of its branches and to the presence of voida (similar to 

 coral reefs) the Lithothamnion algae present exceptional facilities for the 

 multiplying of specific fauna, partly hidden inside the Lithothamnion, partly 

 connected with its surface. Inside the Lithothamnion thrive innumerable 

 Lucernaria (Lucernaria quadricornis), nemerteans (Amphiporus, Cerebratulus) 

 polychaetes (Nereis, Glycera and others), Gephyrea (Phascolosoma eremita, 

 Ph. margaritaceum), Ophiuroidea (Ophiopholis aculeata), holothurians 

 (Phyllophorus pellucidus), young sea urchins, asterids and molluscs (Saxicava 

 arctica, Modiola modiolus). Ascidians (Ciona intestinalis, Pyura aurantium, P. 

 arctica, Sarcobotriloides aureum and others), actinium (Metridia dianthus), 

 polychaetes (Chone infundibuliformis, Leaena abranchiata, Myxicola steen- 

 strupi and Sabella fabricii) are attached to the surface of Lithothamnion. 

 Numerous echinoderms (Ophiopholis aculeata, Cucumaria frondosa) and 

 molluscs (Acmaea virginea, Margarita groenlandica, Chiton ruber, Ch. 

 marmoreus, Ch. albus, Velutina haliotoides, Anomia squamula, Pecten islandi- 

 cus) crawl over the Lithothamnion. The crustaceans (especially some species 

 of Spirontocaris — S. turgida, S. gaimardi, S. spinus and S. polaris), Sclero- 

 crangon boreas, Eupagurus pubescens, Ну as araneus are also numerous on the 

 Lithothamnion. 



Almost 30 years after K. Derjugin's explorations, V. Zatzepin (1962) 

 carried out careful investigations on the quantitative distribution of bottom 

 fauna (1934 to 1936). First of all this worker remarks that the species compo- 

 sition and the distribution of the bottom biocoenoses are on the whole the 

 same as those given by K. Derjugin. The change in the species composition 

 can be easily explained first of all by the rise of temperature, which therefore 

 affected mostly the cliffs, rocks and sandy floors of the northern part of the 



