COMMUNITIES OF THE SEA BOTTOM 341 



fleoruosa,'^ Nucula tennis, Spisula subtruncata, etc., are found gen- 

 erally distributed throughout. The brittle stars are represented by 

 one or more species of Ophiura or Araphiura ; Spatangoidea are usually 

 present, represented by Echinocardium, Spatangus, or Brissopsis. An- 

 nelids vary in number, but Nephthys, Aricia, and Glycera are com- 

 monly to be found. 



The community is distributed in the area to the south of Iceland 

 about the British Isles, across the North Sea, about the Danish Penin- 

 sula, and along the west coast of Norway to North Cape. The asso- 

 ciations are those described by Petersen, Davis, Spiirck, Ford et al. 

 The description of typical portions and the mapping of the communi- 

 ties follow Petersen, modified only slightly by the data of other writers 

 who give no maps. Petersen's map is provisional, but confirmed in 

 the main by others. He recognized several communities which, to 

 follow the arrangement used or the communities of Puget Sound, 

 would be regarded as the associations that constitute the biome. They 

 may be briefly described in the order presented by Petersen, and his 

 names are given in parentheses. The community characterized by 

 Sijndosmya (Abra) alba, found locally, is perhaps to be regarded as 

 an ecotone between the Macoma biome and the Echinocardium-Thy- 

 asira biome. (As provisionally arranged here this major community 

 combines Sparck's, Amphiura, Haploop's and Venus gallina commu- 

 nities [Blegvad, 1922, 1923, 1927; Sparck, 1935].) 



Venus-Echinocardium Association {Venus with Echinocardium 

 Community) (Fig. 78). The community occurs in open sandy coasts 

 at an average depth of 10-12 meters. The bivalves, Venus gallina, 

 Tellina fabula, and Montacuta ferruginosa, together with Echinocar- 

 dium cordatum, make up the greater part of the population. Brittle 

 stars are usually present; gastropods are few or wanting. Annelids 

 are represented by Nephthys hombergi which is most abundant 

 (Blegvad, 1930:36), and two to six other species occur. The fishes 

 enumerated as characteristic of the biome are all present, as are other 

 motile forms such as amphipods (Fig. 78). 



Echinocardium- Amphiura Association {Echinocardium- filiformis: 

 E. Fil. Community) (Fig. 79). This occurs at 12-40 meters of water. 

 The bulk of the population is made up of the bivalve, Abra {Syn- 

 dosmya) nitida, the brittle star, Amphiura filiformis, and Echinocar- 

 dium cordatum. Gastropods are relatively few here, except for the 

 genus Turritella (spp.), but the quantity of annelids is large. The 



1 Authors' names are omitted in connection with northeast Atlantic species; 

 all names are listed by Blegvad (1930), and are to be found in many other 

 publications. 



