24 College of Forestry 



the larvae of large water beetles, and crawfishes. Leeches 

 and the larger pond snails are large consumers of mollusks. 

 Frogs, salamanders, newts, the painted, snapping, and other 

 turtles, as well as many ducks and other water birds also 

 obtain a part of their daily food from this class of animals. 

 The Muskrat is a well-known depredator of the mussel beds, 

 and it is said that the Mink and Otter also eat clams 

 occasionally. 



The amount of molluscan food eaten by these animals is 

 not definitely known, though in some cases it is probably 

 large. The nymph of one dragon-fly (Anax junius) has been 

 known to eat 15 per cent of snails (Amnicola). In the case 

 of the leeches, several are known to eat largely of snails,' and 

 one (Glossiphonia complanata) is called the Snail Leech, 

 and feeds largely on small snails. 



Shellfish as Parasites of Fish. The .intimate relation 

 existing between the fresh-water clams (Fig. 10) and fishes 

 has but recently become understood, principally through 

 studies carried on by naturalists at the United States Bio- 

 logical Laboratory at Fairport, Iowa. The young of these 

 clams are known as glochidia and pass a part of their exist- 

 ence attached to some part of a fish. 



The metamorphosis or transformation of the fresh-water 

 mussels or clams is quite as wonderful and as interesting as 

 that of the butterfly or beetle, and also quite as complicated. 

 In the female mussel the gills or breathing organs are modi- 

 fied to form a broad pouch or marsupium into which the eggs 

 are carried soon after being fertilized by the sperm, which 

 is taken in with the water through the lower siphon. After 

 a period of development the eggs become purse-shaped and 

 the gills are swollen and distended by the mass of young or 

 embryos. After the lapse of time, the length varying in 

 different kinds of mussels, the young are discharged into the 

 water and fall to the bottom where they lie with their two 

 shell valves widely open. The next stage is passed in a fish 

 or amphibian (usually the former) which becomes infected 

 by brushing or stirring up water currents at the bottom, 

 which enables the young to come into contact with the gills, 



