246 College of Forestry 
12. Summary. 
It has been: shown in this chapter that many groups of 
fresh-water animals, including insects, crawfishes, leeches, 
snails, frogs, salamanders, turtles, birds, and mammals feed 
upon mollusks and enter into competition with the mollusk- 
eating fish for the available food supply. Boring algze also 
attack the mussels and larger snails, causing them to exerete 
an additional amount of shelly matter to repair these dam- 
ages. ‘To what extent this agency causes the death of mol- 
lusks is not known. Associates are also present in mollusks, 
either as commensals or as true parasites. In many cases 
the mollusk serves as an intermediary host for a worm which 
completes its cycle of development in a fish, bird or other 
animal. 
— ee 
