For one thing, they are
not exactly fish. They
have no vertebrate
(backbone). They
do not have scales or
fins and few species can swim,
most cannot.
The term "fish" to most
people applies to an
aquatic vertebrate
animal more accurately
called "fin fish"
The dictionary
definition is " An
aquatic animal, such as
a mollusk or crustacean,
that has a shell or
shell-like
exoskeleton.
In the culinary world *,
two major groups of
seafood are called
shellfish.
Mollusks - include
clams, oysters, mussels,
conch, snails and
scallops.
Crustaceans - include
shrimp, crabs, lobster
and crawfish.
* (Squid and octopus (cephalopods) are
sometimes considered
shellfish as well.)
Learn More about
Shellfish
<click here>