GENERAL HISTOLOGY

Detailed explanation-1: -sand dollar, any of the invertebrate marine animals of the order Clypeastroida (class Echinoidea, phylum Echinodermata ) that has a flat, disk-shaped body. They are close relatives of sea urchins and heart urchins. The sand dollar is particularly well adapted for burrowing in sandy substrates.

Detailed explanation-2: -Unlike sea stars that use tube feet for locomotion, a sand dollar uses its spines to move along the sand, or to drive edgewise into the sand. On the upper half of the sand dollar’s body, spines also serve as gills.

Detailed explanation-3: -Sand dollars (also known as a sea cookie or snapper biscuit in New Zealand, or pansy shell in South Africa) are species of flat, burrowing sea urchins belonging to the order Clypeasteroida. Some species within the order, not quite as flat, are known as sea biscuits.

Detailed explanation-4: -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. Their flat disk-like shape is an adaptation for life on the sea bottom where they gather detritus.