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Invertebrates

What Is an Invertebrate?

Invertebrates comprise all the animals on Earth without spines, from the tiny zooplankton to the giant squid. There are so many different kinds, and they are so varied in form, that their lack of a spine is often the only characteristic they share. They live in oceans and freshwater, above and below ground. About 97 percent of all animals are invertebrates. The group includes insects, which are by far the most numerous, as well as spiders, worms, snails, centipedes, clams, mussels, jellyfish, squid, and crabs.