Stereom

Part of a series related to
Biomineralization
General Mineralized tissues Remineralisation Biocrystallization Biointerface Biofilm
Exoskeletons (shells) Arthropod exoskeleton cuticle Brachiopod shell Cephalopod shell cirrate shell cuttlebone gladius Lorica Choanoflagellate lorica Protist shell coccosphere coccolith diatom frustule foraminifera test testate amoebae Seashell echinoderm stereom mollusc shell nacre chiton shell gastropod shell small shelly fauna scaly-foot snail shell estuary shells Sponge spicule Test
Endoskeletons (bones) Vertebrate skeleton Bone mineral Ossification
Teeth, scales, tusks etc Limpet teeth Otolith otolithic membrane Scale microfossils Tusk
Calcification amorphous calcium carbonate marine biogenic calcification calcareous nannofossils Aragonite oolitic aragonite sand aragonite sea Calcite microbial calcite precipitation calcite sea Great Calcite Belt
Silicification biogenic silica siliceous ooze diatomaceous earth
Other forms Bone bed Kerogen alginite oil shale Phosphate phosphorite Pyrena
Related Mineral evolution In soil mineralization immobilization Ballast minerals Magnetofossil Magnetosome Magnetotactic bacteria Magnetoreception Microfossils engrailed gene Druse Cupriavidus metallidurans Biomineralising polychaetes Mineral nutrients Microbial mat Fossilization permineralization petrifaction Burgess Shale preservation
Category
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Stereom is a calcium carbonate material that makes up the internal skeletons found in all echinoderms, both living and fossilized forms. It is a sponge-like porous structure which, in a sea urchin may be 50% by volume living cells, and the rest being a matrix of calcite crystals. The size of openings in stereom varies in different species and in different places within the same organism.^[1] When an echinoderm becomes a fossil, microscopic examination is used to reveal the structure and such examination is often an important tool to classify the fossil as an echinoderm or related creature.^[2]

Evolution

Stereom was the first form of biomineralization to evolve in deuterostomes, predating the evolution of spicules in tunicates and