An invertebrate is an animal that does not have a backbone. Ninety-seven percent of all animal species are invertebrates. Insects, Annelids, Mollusks, Echinoderms, Protozoa, Crustaceans, and Arachnids are all invertebrates.
Invertebrates share four common traits:
- They do not have a backbone.
- They are multi-cellular. All the cells have different responsibilities in keeping the animal alive.
- They have no cell walls, like all other animals.
- They reproduce by two reproductive cells, or gametes, coming together to produce a new organism of their species.