4. How does the Whelk obtain its food?
5. Give the names of three one-shelled molluscs.
LESSON XI.
SHELLS AND THEIR BUILDERS (2)
THE MUSSEL AND OYSTER.
As everyone knows, the Mussel and the Oyster live between two hinged
shells. In the last lesson we called them _bi-valve molluscs_, which is
only another way of saying "soft-bodied animals with two shells." Have
you ever opened an Oyster? It is a tug-of-war, your skill and strength
against the muscles of the animal inside the tight shells.
Like the Periwinkle and other shell-builders, these creatures owe their
strong houses to a wonderful _mantle_; but in this case the mantle is in
two pieces instead of one. You can imagine the Periwinkle's mantle as a
tube enclosing the animal's body. The mantle of the Mussel or the Oyster
is in two pieces; and each half forms its own shell.
The Snail, and other one-shelled molluscs, poke their heads out of the
shell when feeding or moving. Oysters and their two-shelled cousins
cannot do this, for the simple reason that they have no heads!
In some places you see that the rocks at low tide are covered with
Mussels.
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