The animals described in this section are probably the most 

 inportant ones to be studied in the futvire. If there shoiild be a major 

 chsinge in numbers, or if any of them should disappear from the river, 

 it vould be an indication that some chauige in the chemical, physical, 

 or biological conditions heid occurred. 



Annelida 



Oligochaeta . The oligochaetes (worms) occur in both ewiuatic 

 and terrestrial habitats. Members of this class were found throx;ighout 

 the length of the river. Specific identification of these animals is 

 extremely difficult and positive recognition often necessitates perform- 

 ing serial sections. This was not possible during the present study. 



Polychaeta . Most of the polychaetes sure marine or estuarine, 

 but a few are known from fresh water. Neeuithes limnicola was found in 

 the Sacramento River as far upstream as mile 8I.5 (above Sacramento Slough) 

 The greatest numbers, however, were found in the lower area of the river 

 within the zone of tidal influences. 



Crustacea 



Amphipoda . A species of amphipod, Corophium spinicome , was 

 found from mile II8.I to 4.0. This species is generally considered to 

 be a seJLt or brackish water form, and has not been previously reported 

 from fresh water. 



Large numbers of Corophium were taken from the station located 

 at mile 8I.5. At this location the organisms were consistently found 

 burrowed into the clay bottom. A few organisms were found at stations 

 between mile II8.I and mile I8.8, where it again was found in 



-6if- 



