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



shoal, forms typical of the middle part of the Barents Sea are highly developed 

 — Spiochaetopterus typicus, Maldane sarsi, Ctenodiscus crispatus, Astarte 

 crenata, and Arc a glacialis. In the southern parts of the trough the waters are 

 warmer and the warm-water Asychis biceps, Area pectunculoides, Pecten im- 

 brifer, Dentalium striolatum and others are predominant. In the deepest parts 

 of the trough (400 m) the benthos biomass decreases to 5 to 8 g m 2 and less, 

 consisting entirely of infauna forms feeding on ooze. 



Thus in the northern part of the west trough (400 m) and to the east of the 

 Brisaster community, the middle Barents Sea benthic community comes into 

 full development ; it occurs mainly on sandy silt and to a lesser extent on silt 

 and silty sand, at depths of 100 to 350 m. 



The dominant forms of this community are : the polychaete Spiochaetop- 

 terus typicus, the sipunculid PhascoJosoma margaritaceum, the molluscs 

 Astarte crenata and Area glacialis, the echinoderms Ctenodiscus crispatus and 

 Psolus phantapus. Besides this the characteristic forms of the first order are the 

 polychaetes Lumbriconereis fragilis, Nicomache lumbricalis, Myriochele ocu- 

 lata, Maldane sarsi, the molluscs Cardium ciliatum, Macoma calcarea, Saxicava 

 arctica, Axinus flexuosus, the echinoderms Ophioplwlis aculeata, Ophio- 

 cantha bidentata, Ophiura sarsi and Molpadia species. This multiform com- 

 munity, occupying a huge area, can be subdivided into ten variants, differing 

 in their combinations of the above-mentioned forms, and sometimes by the 

 absence of a series of forms, but retaining, nevertheless, an inherent unity. 

 The average biomass of this community is not large — 85-5 g/m 2 — and has the 

 following group composition {Table 61). 



Table 61 



To the east and southeast of the Novaya Zemlya shoal and in the Pechora 

 region, forming a wide belt round the previous community, there lies in the 

 silty sand at shallow depths (50 to 250 m) a community with a preponderance 

 of bivalves. The dominant forms in this belt are : among the molluscs, 

 Astarte borealis, A. montagui, Macoma calcarea, Cardium ciliata, Yoldia 

 hyperborea, Cardium groenlandicum, and among the echinoderms : Ophio- 

 plwlis aculeata and Strongylocentrotus droebachiensis. The characteristic forms 



