Skeletal System of Echinodermata
All Echinodermata consist of an endoskeleton located in the mesodermal, or middle, layer of the skin. The skeleton is mainly made of ossicles, or calcareous (chalky) plates found in the dermis layer of the skin. The skeleton can be fused together and very rigid, or can be flexible and work in unison to help an animal move, among other things. After death, however, the skeletal system usually rots away, especially in those animals who have loosely bound structures, which makes they very difficult to find as fossils. This phylum has shows evolution from the previous phylums as it possesses a skeletal system that will grow with the growth of the organism. There is no need for the organism to shed its skeletal system as the skeletal system is located inside the body, creating no period of extreme vulnerability for the animal and allowing to collectively accumulate nutrients needed to grow rather than excrete their nutrients periodically as waste.