lies between the two sides of the mantle and is attached to it and the adductor muscle.
For shucking oysters, a specially designed knife is inserted between the shell halves to
cut the muscle and thus allow the shell to be opened for removal of the oyster meat.
d. Gills. Four gills extend along the ventral border of the oyster. Gills are the
breathing mechanism for extracting oxygen from the water and releasing carbon
dioxide. At the anterior end, four lips or palps reach under the ends of the gills and
extend forward toward the mouth. The gills are covered on both sides with very fine
hairs (cilia) arranged in rows. These cilia beat back and forth causing a current of sea
water to pass into the gills when the oyster has its shell open. There are small openings
on the surfaces of the gills leading into "watertubes" inside. The beating of the cilia
forces water through these holes and into the watertubes. As the water passes through
the gills, the gills extract oxygen and give off carbon dioxide. Experiments have shown
that one oyster can pump up to 12.7 gallons of water each hour in this fashion. When
the temperature of the water drops to or below 40o F (4o C), the pumping is greatly
reduced, or ceases completely, and the oyster goes into hibernation.
e. Digesting Food. Tiny food organisms in the water are trapped in slime on
the gill surfaces as the water passes through the gills. When these particles become
entangled in the slime, the cilia strike against them in such a way as to roll or slide them
along the gills toward the mouth. Upon reaching the anterior ends of the gills, they are
pushed off, falling between the palps. The palps are also covered with cilia which carry
the particles forward until they slide into the mouth. The mouth too is lined with cilia
which move the food into the stomach. In the stomach, the food is acted upon by the
digestive juices secreted by the digestive gland (liver). The partially digested food is
then passed to the intestine where the nutritive portion is absorbed and the indigestible
portion passed out of the intestines.
f. Spawning. The reproductive organ consists of a mass made up of
microscopic tubes and connective tissue lying between the folds of the intestine and
investing it, as well as the stomach and the liver, in such a manner as to cover the
visceral organs. The branched ducts on the surface over the digestive gland are easily
seen when the oyster is spawning.
2-5. ANATOMICAL FEATURES OF CLAMS
a. General. Clams are moveable bivalves. A clam moves about the shallow
beaches in search of food with assistance of its foot. It is normally covered with sand
and obtains water into its body by extending the siphons above the sandy surface.
Food is obtained in the "filter feeding" manner. The anatomical features are basically
the same as the oyster, with some exceptions. See Figure 2-3.
b. Adductor Muscles. The clam has two adductor muscles, an anterior and a
posterior. Both are used to open and close the shell. There is no locking device as
found in the oyster.