31 



in calcareous rock and a boring sabellid in the outer 

 areas of Zone I, A deep-water boring mollusk, Xylophaga , 

 occurs in water-logged wood» Commensal species may be 

 more frequent than current records indicate, Astropecten 

 (the large sand seastar) harbors two polychaetes, and a 

 small clam is frequently overrun with a creeping hydroid. 

 Parasitic forms have been infrequent or perhaps overlooked. 

 Such are parasitic crustaceans (copepod on Terebellides ; 

 rhizocephalan in Gnathia ) and others. The presence of 

 commensals or parasites with host species can be regarded 

 as a normal or healthy condition , and when one of the 

 association species is absent, it is usually the most 

 dependent one (in such cases, the parasite). 



In Santa Monica Bay it has been found convenient 

 to classify animal associations according to increasing 

 distance from the ends of effluent pipes. Six such areas 

 have been identified, varying with successive distance 

 from an inner zone, at intervals of a half, to several 

 miles. The inner, or most shoreward zone, the Beach- 

 Sand Fauna, is characteristic of much of the strand of 

 Santa Monica Bay, and may be little influenced by the 

 effects of pollution. Only one sample, I W-1, was 

 examined. It contained mainly sand worms, Nephtys 

 calif orniensis , several snails, a sand crab, a prochordate, 

 and numerous smaller sand-dwelling species. All of these 

 species may be dug up along the sandy beach at low tide. 



Sample I W-2, from the bottom under the end of the 



