Invertebrate

Term coined by Chevalier de Lamarck to describe any animal without a backbone?, like insects, squids? and worms.

Invertebrates aren't a coherent group of animals; many of them are much more closely related to Vertebrates? than to the average other Invertebrate. Many better but still unsatisfying divisions of animals were proposed, probably the most popular being to Protostomes, Deuterostomes and all others.

This is one of the places where formal taxonomy and common usage diverge. People tend to think of "things like us" and "everything else." In a very broad sense, "vertebrates" are things like us: they at least have bones, unlike all those weird things. Dividing the world into X and not-X is conceptually appealing and sometimes useful, even when the only thing the not-X have in common is that definition by exclusion.