192 



MARINE ANIMALS 



in this diversified life is recognizable, especially a connection between 

 these biocoenoses and the depth of the water. Other governing factors, 



Fig. 30. — Arrangement of animals on 0.25 sq.m. of sea bottom. II, Echino- 

 cardium-Filiformis community, at a depth of 20-22 m., in the Kattegat. The 

 individuals, numbered for identification, and with the number of individuals, are 

 listed below. Mollusks: (1) Abra nitida, 4; (2) Corbula gibba, 1; (3) Cyprina 

 islandica, 3; (4) Axinus flexuosus, 1; (5) Nucula tenuis, 1; (6) Aporrhais pes 

 pelecani, 1; (7) Turitella terebra, 10; (8) Chaetoderma nitidulum, 1; worms: (9) 

 Glycera sp., 1; (10) Nephthys sp., 6; (11) Brada sp., 5; (12) Terebellides stroemi, 

 3; (13) a fragment of nemertine worm; ophiurids: (14) Amphiura filiformis, 

 60; (15) Ophioglypha albida, juv., 2; (16) O. texturata, 1; sea urchins: (17) 

 Echinocardium cor datum, 5; pennatulids: (18) Virgularia mirabilis, 2. After 

 Petersen. 



as yet unknown, must also exist. Stuxberg 13 distinguished certain sec- 

 tions by the predominance of a single or of few species. C. G. J. Peter- 

 sen 14 has described the composition of eight types of bottom biocoe- 

 noses in the ocean surrounding Denmark; Figs. 29-32 give a good 



