Beginners' zoology . Pearl divers. CHAPTER IX MOLLUSCS The Fresh-water Mussel Suggestions. — The mussel is usually easy to procure fromstreams and lakes by raking or dredging. In cities the hard-shelled clam, or quahog, is for sale at the markets, and the follow-ing descriptions apply to the anodon, unio, or quahog, withslight changes in regard to the siphons. Mussels can be keptalive for a long time in a tub with sand in the bottom. Pairs ofshells should be at hand for study. External Features. — The shell is an elongated oval,broader and blunter at one end (Fig. i88). Why doesthe animal clos
Beginners' zoology . Pearl divers. CHAPTER IX MOLLUSCS The Fresh-water Mussel Suggestions. — The mussel is usually easy to procure fromstreams and lakes by raking or dredging. In cities the hard-shelled clam, or quahog, is for sale at the markets, and the follow-ing descriptions apply to the anodon, unio, or quahog, withslight changes in regard to the siphons. Mussels can be keptalive for a long time in a tub with sand in the bottom. Pairs ofshells should be at hand for study. External Features. — The shell is an elongated oval,broader and blunter at one end (Fig. i88). Why doesthe animal close its shell. Does it open the , Does it thrust the foot forward and pull up to it,or thrust the foot back and push ? (Mussels and clamshave no bones.) Does it go with the blunt end or the moretapering end of the shell forward. (Fig. i88.) Can amussel swim .? Why, or why not 1 97 98 BEGINNERS ZOOLOGY. Fig. i88. — Anodon, or fresh-watermussel. shells for valves in pumps. Lay the shells, fitted together, in your hand with t/ie hingtside away from you and the bhmt end to the lcft{F\g. i88). Is the right or the left shelluppermost. Which is thetop, or dorsal, side .<* Whichis the front, or anterior,end } Is the straight edgeat the top or at the bottom ?Our word ** valve is derivedfrom a word meaning shell,because the Romans usedIs the mussel a univalve or abivalve .- Which kind is the The Does the mussel have bilateral symmetry ? Can youfind a horny covering, or epidermis, over the limy shellof a fresh specimen ? Why is it necessary } Does waterdissolve lime 1 Horn .-* Find a bare spot. Does any ofthe shell appear to be missing there .<* The bare projection on each shell is called the the umbo near the ventral or the dorsal line *. Theposterior or anterior end. Isthe surface of the umbonesworn. Do the umbones rubagainst the sand as the musselploughs i
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