340 MARINE BIOTIC COMMUNITIES 



North Atlantic Communities 



Two communities comparable to the Pandora-Yoldia of the North 

 Pacific are found in the North Atlantic near the European coast. One 

 of them is the Abra community of Petersen, which he indicates is a 

 portion of a larger northern community very evidently sharply dif- 

 ferentiated from the others. The second is widely distributed on the 

 continental shelf of western Europe. Both are bivalve-annelid com- 

 munities with a few brittle starfishes (ophiurids), but neither is rich 

 in annelids. They differ, however, from the Pandora-Yoldia com- 

 munity because of the presence of bilateral sea urchins (Spatangoi- 

 dea) instead of the large starfishes (Asteroidea). 



Petersen (1918) recognized eight communities about Denmark. 

 He furthermore appeared to have them in mind when he prepared a 

 generalized map (1914: App.) of the communities of the North Atlantic. 

 He combined the Echinocardium cordatu7n-Amphiura filiformis 

 (E. Fil.) with the Haploops (Ha), and Brissopsis lyrifera-Amphiura 

 chiajei (B. Ch.), communities and called the resulting major com- 

 munity the Venus community. He thus brought together the several 

 communities with important species in common (binding species) and 

 tacitly recognized the formation as described by most plant ecologists 

 or the biotic formation (biome) as used in this work. The writer has 

 ventured to add Petersen's Brissopsis lyrifera (B.S.) community to the 

 Venus community as suggested by aspect and the occurrence of com- 

 mon or binding species, and to call it the Echinocardium-Thyasira 

 biome. 



Lack of contact with the actual materials has been outweighed by 

 the authors' desire to suggest the parallelism with the grassland asso- 

 ciations and other terrestrial associations and these well-known marine 

 communities. This addition further suggests a resemblance between 

 fishes and the land birds that drift through two or three land biomes 

 in a north and south migration in connection with wintering and 

 breeding. The eel and salmon are comparable to the more spectacular 

 bird migrants. 



Echinocardium-Thyasira Community (Biome) 



This is composed of five or more associations representing Peter- 

 sen's five communities (1915, a, 6:9; Blegvad, 1930:23-55) of the open 

 waters, and others noted by Sparck, Ford, et al. These are all ranged 

 over by cod plaice, haddock, flounder, dab, long rough dab, roa, pipe 

 fish and a few of the gobies etc. Among the bivalves, Thyasira 



