GENERAL HISTOLOGY

Detailed explanation-1: -Description: Echinoidea is a class that belongs to the phylum Echinodermata . Species that belong to this class are the sand dollars, cake urchins, sea urchins, and heart urchins. Echinoids have an egg shaped, circular body which is hemispherical.

Detailed explanation-2: -Diversity. There are about 7, 000 species of living echinoderms and each of them falls into one of five categories. Though most people distinguish between sea urchins and sand dollars, the two are actually members of the same class, Echinoidea.

Detailed explanation-3: -Echinoids are marine animals belonging to the phylum Echinodermata and the class Echinoidea. They have a hard shell (referred to as a test) covered with small knobs (tubercles) to which spines are attached in living echinoids. The test and spines are the parts normally found as fossils.

Detailed explanation-4: -Echinoderms, which are exclusively marine animals, are divided into five classes, the Asteroidea (starfishes), Ophiuroidea (serpent-stars), Echinoidea (sea-urchins, heart-urchins, and sand-dollars), Holothuroidea (sea-cucumbers), and Crinoidea (sea-lilies and feather-stars).