Nearly all animals referred to as worms are invertebrates, including earthworms, and by definition, invertebrates do not have bones. Exceptions include worm lizards, such as the Caecilians and Anguis lizards, which look like worms but have reptilian skeletons.
In addition to earthworms, other boneless animals commonly called "worms" include nematodes, flatworms, priapulid worms and a variety of marine worms, such as bristleworms, bootlace worms and arrow worms. Caterpillars, grubs and maggots are often categorized as worms" too, though they are insect larvae rather than their own worm-bodied species. Worms inhabit nearly every type of environment, acting as an important part of the food chain worldwide.