Mollusca
Three Classes
1. Gastropoda (gastropods)~ slugs and snails
2. Bivalvia (bivalves) ~ clams and other twoshelled shellfish
3. Cephalopoda (cephalopods) ~ squids,
octopuses and cuttlefish
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Bodies of Mollusks
• A mollusk has a soft body which is usually
covered by a hard outer shell.
• Exceptions:
– Slugs and octopuses have lost their shells
through evolution
– Squids have very reduced shells
Anatomy of a Mollusk
• All mollusks have:
– Foot ~ the muscular foot helps it move
– Visceral mass ~ contains the gills, gut, and
other organs
– Mantle ~ covers the visceral mass to protect
the mollusks without shells
• Most mollusks have:
– Shell ~ protects the mollusk from predators and
keeps land mollusks from drying out.
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Symmetry of Mollusks
• Mollusks have bilateral symmetry.
– The two halves of the body mirror each other.
Anatomy of a Snail (gastropod)
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Anatomy of a Clam (bivalve)
Anatomy of a Squid
(cephalopod)
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Eating Behaviors
• Bivalves (clams) ~ filter tiny plant and
bacteria from the water
• Gastropods (snails) ~ eat with a radula
(tiny tongue covered with teeth.
– The radula is used to scrape algae off rocks
and pieces of leaves and seaweed
• Cephalopods (squid) ~use tentacles to grab
their prey and put it in their powerful jaws.
Blue-ringed octopus
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Market Squid
Moon Snail chasing its food
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Achatina fulica
Giant African Land Snail
The largest land snail known is the Giant
African Land Snail. It can weigh up to 2
pounds and be 15 inches long.
Commonly Eaten Mollusks
cockles
conch
oysters
clams
scallops
abalone
whelks
Mussels
Pen shells
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