Soft-bodied organisms are animals that lack skeletons, a group roughly corresponding to the group Vermes as proposed by Carl von Linné. All animals have muscles but, since muscles can only pull, never push, a number of animals have developed hard parts that the muscles can pull on, commonly called skeletons. Such skeletons may be internal, as in vertebrates, or external, like in arthropods. However, a large number of animals groups do very well without hard parts. This include animals like earthworms, jellyfish, tapeworms, squids and an enormous variety of animals from almost every part of the kingdom Animalia.