f. Difference from Finfish. The one difference in the chemical composition of
shellfish and finfish is that some shellfish contain a measurable amount of
carbohydrates while finfish do not.
2-3. INTRODUCTION TO MOLLUSKS
a. General. Mollusks are defined as shellfish having soft, unsegmented bodies
commonly covered by a hard outer shell. Those with a shell of one piece are called
univalves while those with shells of two pieces are bivalves. The shell of the bivalves
open and close for normal body function. See Figure 2-1. Mollusks of interest to food
inspectors include oysters, clams, and scallops. Mussels, abalone, and squid are of
commercial importance, but they are not procured by DOD.
Figure 2-1. Mollusks
b. Oysters. Oysters are bivalve mollusks found in most coastal waters, except
in the polar seas. They prefer tidal regions, particularly estuaries where the salinity of
the sea water is reduced by fresh water rivers. Oysters cannot move about after they
have attached themselves at the bottom of a tidal region.
c. Clams. Clams, like oysters, are bivalves. The term "clam" includes a number
of different species found all over the world. Many clams are able to dig down into the
bottom, and, to a certain extent, move around.
d. Scallops. Scallops are found in all seas of the world. They are free-
swimming and propel themselves through the water by rapidly opening and closing their
shell. Scallops are found in deep or shallow water. In the United States, there are only
two species of commercial importance: the Bay scallop and the Deep Sea scallop.