Abstract
The skeleton of echinoids is internal and mesodermal, as in other echinoderms. Skeletal elements, including spines, are covered with single-layer epidermis and the skeleton is functionally external relative to the main body of the animal. It is composed of calcite with a high content of magnesium. Skeleton parts vary in the amount of magnesium, depending on the sea water temperature. However, at the relatively low taxonomic level, the major factor in this respect is genetic control. Representatives of different taxonomic groups living in the same temperature conditions differ considerably in the content of magnesium. Spongy or fenestrate microstructure called stereome is rather specific. Other type of microstructure is only characteristic of some elements of the Aristotle’s lantern. Cristallographically, each element is a single calcite crystal with definite orientation of optical axes. The formation of larval skeleton begins at the late blastula stage. The larval skeleton is rather specific and sometimes varies in different species of the same genus. The development of definitive skeleton is either connected with elements of larval skeleton or it is formed independently in the amniotic cavity on the left side of the larva.
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Solovjev, A.N. Echinoid skeleton. Paleontol. J. 48, 1540–1551 (2014). https://doi.org/10.1134/S0031030114140135
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DOI: https://doi.org/10.1134/S0031030114140135