Invertebrates, which outnumber humans by up to 10 million to one, have hundreds of species threatened with extinction by means of both natural events and human activities (habitat alteration, pollution, introduction of exotic animals and plants, and exploitation). Invertebrate organisms play the key role in supporting the complex food chains of the seas and oceans, only on land do large grazing animals dominate. Any disturbance of ecological balance can lead to a situation in which some species of invertebrates form uncontrolled over-expanding population damaging other species.
An invertebrate is any animal lacking a backbone or bony segment that encloses the central nerve cord.