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.

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: -Sand dollars belong to Phylum Echinodermata and Class Echinoidea which includes sea urchins and heart urchins. Features: They got their name because they resemble a one-dollar coin. Like other echinoderms, sand dollars are symmetrical along five axes, and have tube feet and spines.