Collagen

In vertebrates, which include all animals with a backbone, connective tissues are highly organized and developed. In invertebrates, which include the animals without backbones, connective tissues are not as well organized. However, in nematodes, also known as roundworms (an invertebrate animal), collagen plays a role in movement. The outer covering of the nematode, called the cuticle, consists primarily of collagen. The collagen helps the nematode move and also imparts some longitudinal elasticity. Because the collagen fibers crisscross each other and are not parallel in the nematode cuticle, nematodes are limited in side-to-side movement.