GENERAL HISTOLOGY

Detailed explanation-1: -Echinoidea is a clade of marine animals including sea urchins, heart urchins, sand dollars and sea biscuits. Found in benthic habitats across all latitudes, echinoids are key components of marine communities such as coral reefs and kelp forests.

Detailed explanation-2: -Sand dollars-flattened sea urchins adapted to life on the shifting sand-use thousands of tiny spines to move about and burrow into the seafloor.

Detailed explanation-3: -Sand dollars and sea urchins both belong to the phylum Echinodermata, a group which contains other radially symmetrical animals such as starfish and sea cucumbers. Unlike starfish and sea cucumbers, sea urchins and sand dollars belong to the same class: Echinoidea.

Detailed explanation-4: -There are several distinct groups of echinoderms related to sea stars. Sea urchins and sand dollars are grouped together because they have large solid plates that form around their soft bodies.

Detailed explanation-5: -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.