| About
the Phylum Mollusca The word
"Mollusca" comes from the Latin molluscus,
or soft.
Including such diverse animals as
snails, oysters and octopuses, this is one of the most
familiar of all the large animal groups.
Characteristics (1) Calcareous
shell with underlining mantle of tissue; (2) ventral,
muscular foot; (3) gut with two openings; (4) body
cavity.
Size Less than an inch to 55
feet in the giant squid.
Habitat All waters and land.
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Class
Monoplacophora -- Neopilina (3 species) --
Living members of this class, thought extinct for
300 million years, were first collected in 1952
from a deep ocean trench at 11,778 feet.
Subsequent finds indicate their distribution may
be worldwide in deep seas. Most species are a
scant inch long, with a single cap-shaped shell
and a broad, flat foot. |
Class
Amphineura -- chitons (about 600 species) --
With a large flat sucker-foot and heavy mantle
margin, chitons cling to rocky shores,
particularly in the Pacific Northwest, scraping
up algae. One to 12 inches long, they are
protected by a shell of eight overlapping
pictures. |
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Class Gastropoda -- snails (about 100,000 species) --
This is the largest class of mollusks. Marine
species include snails, conches and sea slugs.
Fresh-water snails have both gillbearing and
airbreathing species; the 19,000 species of land
snails have a cavity beneath the mantle adapted
as a lung. A broad, flat foot, a distinct head
with tentacles and a spirally twisted shell are
generally typical of this class. |
Class Bivalvia -- bivalves (about 30,000 species) --
Including the clams, oysters and scallops, the
bivalves have a laterally flatenned body enclosed
within two hinged shells. Most are marine, though
some are found in fresh water. |
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Class
Scaphopoda -- tusk shells (about 200
species) -- The one- to two-inch tusk shells
burrow head first in the sea bottom. The tapered
end of the shell projects above the sand surface,
and water for respiration is pumped into and out
of its opening. Scaphopods feed on small
organisms caught by many little tentacles on the
head. |
Class
Cephalopoda --
octopus, squid, nautilus (about 1,000 species) --
Eight or more suction-cupped tentacles enable
cephalopods to seize prey. A water jet from a
funnel propels them. Nautilus alone has an
external shell. Most of the class are under two
feet in length, but the Atlantic giant squid
reaches 55 feet. |
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