Editing Skeleton (section)

=== Echinoderms ===
The skeletons of [[echinoderm]]s, such as [[starfish]] and [[sea urchin]]s, are endoskeletons that consist of large, well-developed [[sclerite]] plates that adjoin or overlap to cover the animal's body. The skeletons of [[sea cucumber]]s are an exception, having a reduced size to assist in feeding and movement. Echinoderm skeletons are composed of [[stereom]], made up of [[calcite]] with a [[monocrystal]] structure. They also have a significant [[magnesium]] content, forming up to 15% of the skeleton's composition. The stereome structure is porous, and the pores fill with connective [[Stromal cell|stromal]] tissue as the animal ages. Sea urchins have as many as ten variants of stereome structure. Among extant animals, such skeletons are unique to echinoderms, though similar skeletons were used by some [[Paleozoic]] animals.<ref>{{Cite journal |last1=Kokorin |first1=A. I. |last2=Mirantsev |first2=G. V. |last3=Rozhnov |first3=S. V. |date=2014-12-01 |title=General features of echinoderm skeleton formation |url=https://doi.org/10.1134/S0031030114140056 |journal=Paleontological Journal |language=en |volume=48 |issue=14 |pages=1532–1539 |doi=10.1134/S0031030114140056 |bibcode=2014PalJ...48.1532K |s2cid=84336543 |issn=1555-6174}}</ref> The skeletons of echinoderms are [[mesoderm]]al, as they are mostly encased by soft tissue. Plates of the skeleton may be interlocked or connected through muscles and ligaments. Skeletal elements in echinoderms are highly specialized and take many forms, though they usually retain some form of symmetry. The spines of sea urchins are the largest type of echinoderm skeletal structure.<ref>{{Citation |last1=Nebelsick |first1=James H. |title=Echinoderms: Hierarchically Organized Light Weight Skeletons |date=2015 |url=https://doi.org/10.1007/978-94-017-9398-8_8 |work=Evolution of Lightweight Structures: Analyses and Technical Applications |pages=141–155 |editor-last=Hamm |editor-first=Christian |place=Dordrecht |publisher=Springer Netherlands |language=en |doi=10.1007/978-94-017-9398-8_8 |isbn=978-94-017-9398-8 |access-date=2022-07-31 |last2=Dynowski |first2=Janina F. |last3=Grossmann |first3=Jan Nils |last4=Tötzke |first4=Christian|series=Biologically-Inspired Systems |volume=6 }}</ref>