Invertebrates
Of the million or more animal species in the world,
more than 98% are invertebrates.Invertebrates don't have an internal skeleton
made of bone. Many invertebrates have a fluid-filled, hydrostatic skeleton,
like the jelly fish or worm. Others have a hard outer shell, like insects and
crustaceans. There are many types of invertebrates. The most common invertebrates
include the protozoa, annelids, echinoderms, mollusks and arthropods. Arthropods
include insects, crustaceans and arachnids.