12. ECOLOGY 125 



sharply in numbers over the other forms in the complex biocoenosis, of 

 which almost all the sedentary representatives (Coelenterata, Porifera, 

 Ascidiacea and Bryozoa) dwell on the tubes of the pogonophores. Amongst 

 the carnivorous species of this biocoenosis the anomuran decapod crustacean 

 Munidopsis apparently feeds on Polybrachia (M. Sokolova, unpublished). 



Since they are sedentary filter-feeders pogonophores probably depend to 

 a considerable degree on the amount of food particles suspended in the water 

 and on the bacterial flora developed in it. They are therefore most numerous 

 in those places where there is a more or less continuous local concentration 

 of organic matter near the bottom depending on a swift steady bottom current 

 and on the conformation of the sea bed (Sokolova, 1956). This is also quite 

 clear from the fact that in land-locked seas and in deep trenches the pogono- 

 phoran fauna is far more diverse than in the open reaches of the ocean far 

 from continental land-masses. [It may also be useful to speculate that the 

 conditions which Pogonophora need to meet their food requirements may be 

 met in two other ways also. Firstly, an area of convergence of two surface 

 currents may lead to a steady down-flow of surface water relatively rich in 

 plankton: some of the pogonophores found in the subantarctic far from land 

 appear to be situated in regions of the Subantarctic Convergence (see Fig. 

 87). Secondly, cascading of water down canyons in the continental slope may 

 also provide abundant food : the Pogonophora collected off the mouth of the 

 English Channel were found in just such places — D.B.C.] 



It is doubtful whether pogonophores ever leave their tubes, so that they 

 cannot adapt to free life in the open. Inside the tube, however, they are 

 probably active and swift-moving, now poking the front end of the body, with 

 the tentacular apparatus, out of the tube, now drawing it back in again. In 

 this respect they recall the sedentary tubicolous polychaetes. The long tube is 

 always considerably longer than the animal itself and does not impede its 

 mobility. The numerous adhesive papillae, with their associated cuticular 

 plaques, serve to support it against the inner wall of the tube. The strong 

 development of the longitudinal dermal musculature and the greater length 

 of the animal when fixed inside the tube than when fixed out of it indicate its 

 tremendous ability to extend and contract. Thrusting out the front end of the 

 body from the tube is possibly accomplished by great extension of the trunk, 

 whose hind part remains firmly attached to the walls of the tube by means of 

 the toothed platelets of the girdles. When irritated or when danger threatens 

 from outside the animal apparently disappears in a flash into the depths of 

 the tube in consequence of the simple contraction of the longitudinal muscu- 

 lature and the steadfast adhesion of the girdles to the tube walls, an action 



