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An invertebrate is an animal lacking a vertebral column. The group includes 98% of all animal species[1] — all animals except those in the Chordate subphylum Vertebrata (fish, reptiles, amphibians, birds, and mammals). Invertebrates form a paraphyletic group. (For a full list of animals considered to be invertebrates, see animal.) All the listed phyla are invertebrates along with two of the three subphyla in Phylum Chordata Urochordata and Cephalochordata. These two, plus all the other known invertebrates, have only one cluster of Hox genes, while the vertebrates have duplicated their original cluster more than once. Within paleozoology and paleobiology, invertebrates big and small are often studied within the fossil discipline called invertebrate paleontology. name="External_links" id="External_links">
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Invertebrate Subcategories
Invertebrate Articles
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