Invertebrates

An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata (fish, amphibians, reptiles, birds, and mammals).

Invertebrates form a paraphyletic group. Given a common multicellular, eukaryotic ancestor, all contained phyla are invertebrates along with two of the three subphyla in Phylum Chordata: Tunicata 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.

Books

<a href="/book/ecology-acanthocephala">Ecology of the acanthocephala</a>
Kennedy, Clive Russell
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