They are bilateral, soft-bodied, and possess a coelom. Most have a head, a foot, gills, and a shell or a reduced version of one. A mantle drapes over the body and secretes the shell. Most have a fleshy foot. Many have a radula for shredding food.
Gastropods include
snails
and slugs . Gastropod literally means "belly
foot" which describes the position of the digestive tract within the
large muscular foot .
Most of the other organs are located in the spiraled shell. Embryonic torsion in gastropods places
several organs toward the head end of the body. Torsion is a twisting of body parts during larval
development. Before torsion, the head faces forward and the anus faces backward. After torsion,
the anus is positioned over the head.
Gastropod video taken at the Monterey Bay Aquarium. Look closely and you can see the radula at the anterior end.
Bivalves include
clams ,
scallops ,
and
oysters .
The shell of two parts encloses the body. The mother-of-pearl lining of the shell may generate
pearls. In bivalves, there is no head, but a large foot specialized for burrowing comprises the
bulk of the body. Water and suspended food are drawn in through siphons by the action of the cilia
on the gills.
Cephalopods include
squid,
octopus,
cuttlefish, and
nautilus.
This group includes the largest invertebrates known. The
giant squid
can attain a length of over sixty feet. They are also the most intelligent of invertebrates,
having large brains relative to their body size. Only the nautilus retains an external shell. The
cephalopod body
is modified for a highly active predatory life-style and includes tentacles, beaklike jaws, and
jet propulsion by mantle contractions. In jet
propulsion, water is forced out of the mantle cavity through a funnel-shaped siphon.
Thie video (Audio - Not Important) of cuttlefish was taken at the Monterey Bay Auqarium.
Octopus video (Audio - Not Important) taken at the Monterey Bay Aquarium.
Videos of Nautilus at the Monterey Bay Aquarium taken from the side and from the front
REVIEW: A mantle is found only among the
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