Circular No. 9—1921—Common Garden Insects and their Control
Pearl divers.
CHAPTER IX
MOLLUSCS
The Fresh-water Mussel
Suggestions.—The mussel is usually easy to procure from streams and lakes by raking or dredging. In cities the hard-shelled clam, or quahog, is for sale at the markets, and the following descriptions apply to the anodon, unio, or quahog, with slight changes in regard to the siphons. Mussels can be kept alive for a long time in a tub with sand in the bottom. Pairs of shells should be at hand for study.
External Features.—The shell is an elongated oval, broader and blunter at one end (Fig. [188]). Why does the animal close its shell? Does it open the shell? Why? Does it thrust the foot forward and pull up to it, or thrust the foot back and push? (Mussels and clams have no bones.) Does it go with the blunt end or the more tapering end of the shell forward? (Fig. [188].) Can a mussel swim? Why, or why not?
Fig. 188.—Anodon, or fresh-water mussel.
Lay the shells, fitted together, in your hand with the hinge side away from you and the blunt end to the left (Fig. [188]). Is the right or the left shell uppermost? Which is the top, or dorsal, side? Which is the front, or anterior, end? Is the straight edge at the top or at the bottom? Our word “valve” is derived from a word meaning shell, because the Romans used shells for valves in pumps. Is the mussel a univalve or a bivalve? Which kind is the oyster? The snail?