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. Click on the picture or name of the animals below for more information.