Invertebrate
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Invertebrate is a term coined by Jean-Baptiste Lamarck to describe any animal without a spinal column. It therefore includes all animals except vertebrates (fish, reptiles, amphibians, birds and mammals).
Invertebrate are classified into over 30 phyla, from simple organisms such as sponges and flatworms to complex animals such as arthropods and molluscs.
Since invertebrates include all animals except a certain group, invertebrates form a paraphyletic group, but, despite not forming a "natural group" (that is, monophyletic), "invertebrate" is still a widely used term. It is not uncommon for books entitled "Invertebrate Zoology" to be found. This reflects the bias in society and also in zoology towards larger, more complex animals that are more closely related to humans. Thus, there are relatively many scientists studying (and relatively much funding available for the study of) birds, mammals, reptiles, and so on, but far fewer scientists studying invertebrates, even though invertebrates include 97% of all animal species.
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.