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Pelecypoda
This class includes the Mollusca having a shell consisting of two valves.
Movement may he by means of a plough-like muscular foot. Plume = or
plate = like gills are present, and there may also be tubular siphons, for
taking in and throwing out water for respiration. Most of the economically
important Molluscs are from this class, such as the oysters, clams, and
mussels, all of which comprise the shell fishery . The pearl oyster,
although not normally used for food, is equally important commercially
because of the pearls it yields. In this class are also the marine woodborers
which cause considerable damage to wooden boats, piers, etc.
Gastropoda
The body is asymmetrical, with a well-developed muscular foot. A head
with eyes and tentacles is present. Majority have a spirally twisted shell. In
some, this may be concealed (e. g. Aplysia) within the body. In this class
are the snails, shells of which are popular with collectors. Larger and small
varieties of snails are eaten
Scaphopoda
Popularly called elephant's tusk shells, they have an elongated body with
bilateral symmetry, inside a tubular shell with open ends.
Cephalopoda
Highest developed of all Mollusea, there is a distinct head, with well
developed eyes, surrounded by 8 to 10 tentacles. The body is bilaterally
symmetrical. A shell may be present. They are active animals, e.g. squid,
cuttlefish, octopus.
FAUNA 207