GENERAL HISTOLOGY

Detailed explanation-1: -Sea urchins and sand dollars are examples of Echinoidea.

Detailed explanation-2: -Sea urchins are members of the phylum Echinodermata, which also includes sea stars, sea cucumbers, sand dollars, brittle stars, and crinoids.

Detailed explanation-3: -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-4: -Examples of echinoderms include sea stars, sea urchins, sea cucumbers, brittle stars, and feather stars (Fig. 3.83). Although they may appear very different, echinoderms all have two major defining characteristics that set them apart from all other animals: a water vascular system and five-sided radial symmetry.

Detailed explanation-5: -Sea urchins are in the Echinodermata phylum. The scientific name is Echinoidia, which is also the name of their class. They are in the Camarodonta order, and some belong to the Echinidae family. This family contains genera including Strongylocentrotus and Lytechinus.