SURVEY OF INVERTEBRATES 89 



Besides living in the above-mentioned anaerobic habi- 

 tats, clams also frequently occur in localities where the 

 oxygen supply is scanty. Cole (1926) found Anadon- 

 toides ferrussacianus buried from two inches to a foot 

 deep in soft nmck consisting mainly of decomposing plant 

 material and fine silt. The oxygen content of the water 

 permeating the mud was only about 6 per cent of that of 

 the stream water. The animals were nevertheless active 

 and most of them had their foot extended. Another sim- 

 ilar case is that of Anodonta mutabilis which was found 

 alive by Fehlmanu (1917) in water containing only 0.081 

 cc. of oxygen per liter. 



It seems very unlikely that animals found under such 

 conditions could have maintained a purely aerobic me- 

 tabolism. While the oxygen consumption of these clams 

 seems not yet to have been studied in relation to the ten- 

 sion, it is to be noticed that Maloeuf (1937) found a 

 clear case of dependency in Mytilus edulis and Nozawa 

 (1929) a less marked one in Ostrea circumpicta. 



Unlike Pisidium, Anodonta extends its foot and be- 

 gins to wander around w^ien the oxygen of the water is 

 almost depleted (Alsterberg, 1930). Sphaeriuni cor- 

 neum behaves still differently. Jatzenko (1928) im- 

 mersed some of these clams in tightly closed containers 

 which had been filled with water rich in oxygen. During 

 the first day they had their siphons extended and their 

 shells open. After they had consumed some oxygen and 

 thus lowered the oxygen tension of the water, they 

 closed their shells and kept them closed for 18 days. Later 

 on, however, they began again to crawl around and their 

 locomotion became increasingly active until the experi- 

 ment was discontinued at the end of 46 days (from the 

 start). This observation might be interpreted as indi- 

 cating an adaptation to the anoxic conditions, but the 

 present writer would prefer to accept such an explanation 

 only after Jatzenko 's results have been confirmed. 



