page_title: Sclerite
section_title: Prehistory
hierarchical_section_title: Sclerite / Prehistory
caption_attribution_description: English: Fossil specimen of Wiwaxia from the Burgess Shale on display at the Smithsonian in Washington, DC.
context_page_description: A sclerite is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instead it refers most commonly to the hardened parts of arthropod exoskeletons and the internal spicules of invertebrates such as certain sponges and soft corals. In paleontology, a scleritome is the complete set of sclerites of an organism, often all that is known from fossil invertebrates.
context_section_description: A scleritome is a skeleton made of isolated elements, like the scales of organisms such as the halwaxiids, the teeth in a radula, spicules in a sponge skeleton, or the elements in a conodont apparatus. The term was coined by the palaeontologist Stefan Bengtson.
  Although sclerites are of considerable importance in the study of extant animals, in palaeontology they are of far greater relative importance because they often are the only parts of an animal that fossilise at all, let alone well or clearly. Many extinct groups are known only from sclerites, leaving moot the question of what their gross anatomy might have looked like.
  An example of the use of the term in paleontology is to describe hollow calcium carbonate, calcium sulfate or calcium phosphate plates grown as body armor by a number of Early Cambrian animals. Unlike sponge spicules, Early Cambrian sclerites appear to be external armor rather than internal structural elements. Sclerites are found on a curious collection of early animals including a common spongelike animal called Chancelloria; an armored slug-like form Wiwaxia; an armored worm with a pair of brachiopod-like shells Halkieria; and another armored worm Microdictyon that is generally considered to be a lobopod/onychophore.
  It has been suggested that the sclerites of the Cambrian Wiwaxia are homologous with the bristles of annelid worms.
  At least one modern gastropod mollusc living near deep sea hydrothermal vents has structures made of iron sulfides similar to some Cambrian sclerites.
caption: The fossilized scleritome of Wiwaxia corrugata
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