GENERAL HISTOLOGY

Detailed explanation-1: -Although these spines may look like components of an exoskeleton at first glance, echinoderms do not have an exoskeleton. Instead, the spines are extensions of an internal endoskeleton. The endoskeleton is composed of calcium carbonate plates and spines that are actually covered by a thin layer of epidermis (skin).

Detailed explanation-2: -Echinoderms possess a unique internal skeleton (or endoskeleton) composed of thousands to millions of calcium carbonate components known as ossicles. Similar to a complicated 3-D puzzle, these pieces are infused with tissue and covered by an epidermis, or skin like covering.

Detailed explanation-3: -Echinoderms are marine invertebrates. They include sea stars, sand dollars, and feather stars. Echinoderms have a spiny endoskeleton. They have radial symmetry as adults but bilateral symmetry as larvae.

Detailed explanation-4: -Ossicles are small calcareous elements embedded in the dermis of the body wall of echinoderms. They form part of the endoskeleton and provide rigidity and protection. They are found in different forms and arrangements in sea urchins, starfish, brittle stars, sea cucumbers, and crinoids.

Detailed explanation-5: -The endoskeleton of echinoderms (Deuterostomia: Echinodermata) is of mesodermal origin and consists of cells, organic components, as well as an inorganic mineral matrix.