196 



GENERAL ZOOLOGY 



If they are fortunate enough to fall near the shore line, 

 they anchor themselves to a seaweed, or to a pebble, by a 

 tough, gelatinous thread (Fig. 103, 3) which is secreted 

 by a gland at the base of the foot (Fig. 103, 1). This thread 

 is called the byssus. In certain mussels found in the sea the 

 byssus is a permanent and very complicated organ of the 



adult, but in Mya are- 

 naria it disappears when 

 the clam is about five 

 millimeters (one fifth of 

 an inch) long. At that 

 time the animal burrows into the 

 mud and sand, where it usually re- 

 mains permanently. 



Relation to Environment. The adult 

 Mya arenaria lives in soft mud and 

 sand between high-tide line and a 

 few feet beyond low-tide line. The 

 reason the clam lives in that situa- 

 tion is because food is most abun- 

 dant there. Lying almost helpless 

 in its mold of mud, the long-neck 

 clam is rendered in a measure in- 

 dependent of conditions outside, as long as the currents of 

 water carry the bountiful supplies of food over its burrow. 

 Although the clam is not so highly esteemed as an article 

 of human food as its relative the oyster, it is nevertheless 

 of great value. 



The American Oyster 



Habitat and Distribution. The American oyster {Os'trea 

 virgin'ica, Fig. 104) is found in shallow to deep water 

 along the Atlantic coast from the Gulf of Mexico to Mas- 

 sachusetts Bay. As the artist has shown in the picture, the 



Fig. 103. Young long-neck 

 clam 



1, foot; 2, siphon; 3, byssus 



thread; U, pebbles. (After 



J. L. Kellogg) 



