Invertebrates are animals with no internal skeleton or backbone. Invertebrates make up about 95% of all animal species on Earth. Types of invertebrates include annelids, arachnids, cnidaria, crustaceans, echinoderms, insects, mollusks, and protozoa. Exceptions include amphibians, birds, fish, mammals, marsupials, and reptiles, which are vertebrates with an internal backbone.
Many invertebrates have a fluid-filled skeleton like the jellyfish or worm. Other invertebrates have a hard outer shell, like insects and crustaceans.
For more information on invertebrates see the Kidport Invertebrate Reference Library.