An invertebrate is an animal without a backbone. The group includes 95% of all animal species[1] – all animals except those in the chordate subphylum Vertebrata (fish, amphibians, reptiles, birds, and mammals).
Invertebrates form a paraphyletic group. 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.
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Subject: An invertebrate is an animal without a backbone 
Mon Mar 21, 2011 11:33 pm