GENERAL HISTOLOGY

Detailed explanation-1: -Echinoderm skeletons are composed of high-magnesium calcite having a fenestrate structure. Each skeletal ossicle appears to be a single crystal of calcium carbonate rather than a polycrystalline aggregate as, for example, are mollusc shells.

Detailed explanation-2: -Echinoderms possess a unique internal skeleton (or endoskeleton) composed of thousands to millions of calcium carbonate components known as ossicles.

Detailed explanation-3: -Stereom is a calcium carbonate material that makes up the internal skeletons found in all echinoderms, both living and fossilized forms.

Detailed explanation-4: -Echinoderms also have calcium carbonate endoskeletons, ranging from microscopic spicules in sea cucumbers to visible plates in sea stars and urchins. Most echinoderms have a complete digestive system and a large coelom.

Detailed explanation-5: -The ossicles are composed of high magnesium calcite, a polymorph of calcium carbonate, commonly organized into a porous microstructure called stereom [12].