Most mollusks have a soft, skin-like organ covered
with a hard outside shell. Some mollusks live on land, such as the snail and slug. Other mollusks live in water, such as the oyster, mussel, clam, squid and octopus.
Land living mollusks, like the snail, move slowly on a flat sole called
Ocean living mollusks move or swim by jet propulsion. They propel themselves
by ejecting water from their body. For example, the squid ejects a jet of water
from a cavity within its body, and the scallop ejects water to move by
clamping its shell closed.