GENERAL HISTOLOGY

Detailed explanation-1: -All echinoderms are marine. They have a calcareous endoskeleton, consisting of numerous small plates covered by a thin epidermis. They are probably the first animals to have evolved an endoskeleton derived from mesodermal tissue.

Detailed explanation-2: -Echinoderms evolved from animals with bilateral symmetry. Although adult echinoderms possess pentaradial symmetry, their larvae are ciliated, free-swimming organisms with bilateral symmetry. Later, during metamorphosis, the left side of the body grows at the expense of the right side, which is eventually absorbed.

Detailed explanation-3: -Echinoderm skeletons are made up of interlocking calcium carbonate plates and spines. This skeleton is enclosed by the epidermis and is thus an endoskeleton. In some, such as sea urchins, the plates fit together tightly.

Detailed explanation-4: -place the origin of echinoderms in the late Precambrian, at around 570 Ma and several 10 s of millions of years before the first articulated specimens are found.

Detailed explanation-5: -Echinoderms are a phylum of marine invertebrates that include starfish, brittle stars, sea cucumbers, sea urchins, sand dollars, and crinoids.