SEA-FISHERIES LABORATORY. 141 



(Montagu) is fairly common on the cockle beds in the Dyfi 

 Estuary. 



Cercariae of a number of species of parasitic Trematodes 

 occur among the species enumerated, especially C. edule, 

 M. edulis, L. littorea, P. stagnalis and C. maenas. The only 

 species I have obtained is Cercaria ubiqnita from P. stagnalis, 

 at Ynyslas, Aug. 25th, 1918. Miss Lebour gives the host as 

 C. maenas. 



Prof. Herdman* mentions having found many cockles 

 infected with a minute Copepod, Lichomolgus agilis, which he 

 regards as a commensal. 



A complete list of all the species inhabiting a cockle bed 

 would run to some length, including as it would many 

 Foraminifera, Diatoms, etc. 



The inter-relations of all these forms and their parasites 

 form a most interesting cycle. As regards food Johnstonet 

 states that the cockle feeds upon Algal spores, etc., etc., and 

 this probably applies to all the bivalves mentioned. The food 

 of Arenicola has already been mentioned. Littorina and 

 Paludestrina are likewise vegetable feeders. 



The Crustacea are generally carnivorous or omnivorous. 

 EhrenbaumJ (quoted by Petersen and Jensen, 1911) states 

 that larval forms contain Diatom skeletons and are probably 

 detritus feeders, while adults either feed on mud from the 

 bottom, or on worms, Amphipoda, Schizopoda, etc. 



Herdman § considers that Macoma and Cardium are both 

 of very great importance in furnishing food to the fry of flat 

 fish at a time when they first become ground feeders, and leave 

 off eating Copepoda. Adult flat fish (plaice, flounder, etc.) 

 also feed largely upon the beds during high tide. The food of 



* Report Lancashire Sea-Fish. Lab. 1892. 

 f Report Lancashire Sea-Fish. Lab., L899. 

 J Zur Naturgeschichte von Crcmgon wilgM 

 § Op. cit.1893. 



