200 GENERAL ZOOLOGY 



into definite and usually unfavorable relations to them. Only- 

 one of these animals, so far as known, is anything but harm- 

 ful to the oyster. That one is a little crab, about thirteen 

 millimeters (half an inch) wide, which spends its life in the 

 mantle cavity of its messmate. The greatest enemy of the 

 adult oyster is the starfish (Fig. 124). There are various 

 boring snails, which make round holes through one of the 

 valves with their rasping tongues and draw out what they 

 need of the soft parts (compare Fig. 119). Another enemy 

 is the boring sponge, which, as it grows, makes holes in the 

 valves by a secretion which it produces. Like most other 

 animals, the oyster has its parasites. With all these facts 

 before us, the statement of Professor Moebius regarding 

 the European oyster, that each oyster when born has 

 1145000 °f a chance to survive and reach adult age, 

 seems well within reason. 



The Scallop 



Habitat and Distribution. Of all the shellfish that inhabit 

 the shallow waters of the Atlantic coast of our country, 

 none is more beautiful in color or in line than the common 

 scallop, Pec' ten irra'dians (Fig. 106). Scallops are abun- 

 dant among the eelgrass of shallow bays and inlets from 

 the Gulf of Mexico to Massachusetts Bay. Above the latter 

 region the waters are made colder by the arctic currents. 

 Pecten irradians and many other species of sea animals do 

 not live north of Cape Cod. 



Relation to Environment. The very young scallop holds to 

 some fixed object after the manner of a young soft-shell clam 

 (Fig. 103). The adult scallop has no byssus, and only the 

 rudiment of a foot. The scallop in the foreground of the 

 picture is in what we might call the attitude of rest. It has 

 released its single adductor muscle, which, we may say in 

 passing, is the only part of the animal sold for food. 



