endoskeleton
Endoskeleton An endoskeleton is a skeleton that consists of hard, mineralized structures located within the soft tissue of organisms. An example of a primitive endoskeletal structure is the spicules of sponges. The bones of vertebrates are composed of tissues, whereas sponges have no true tissues Figure 38.4 . Endoskeletons provide support for the body, protect internal organs, and allow for movement through contraction of muscles attached to the skeleton.