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Invertebrates are an extraordinarily diverse group of animals that include over 30 phyla. Invertebrates do not have a backbone, nor a bony skeleton. This large group of animals includes sponges, cnidarians, flatworms, roundworms, segmented worms, molluscs, echinoderms, and arthropods.
A Guide to Vertebrates and InvertebratesAmong the most basic criteria by which animals are sorted is whether or not they possess a backbone. This single trait places an animal into one of just two groups: the vertebrates or the invertebrates and represents a fundamental division among all animals alive today as well as that have long ago disappeared into the ether of the past.
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