THE MAIN INVERTEBRATE GROUPS
The invertebrates, as their name indicates, have no backbone. Their body is soft,
but it is protected on the outside, by a carapace in the case of the crustaceans,
or by a shell in mollusks, or it is supported by an internal calcareous skeleton,
as in corals.
Although they are considered less evolved animals than the vertebrates - the
group to which fish belong - invertebrates sometimes adapt in surprising ways to
ensure their survival. The crustaceans, for example, can walk or swim to look for
food or flee an enemy, while corals and anemones unfurl to capture microparticles,
such as plankton, in open water, or retract to escape their predators.