The Animal Kingdom

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.