GENERAL HISTOLOGY

Detailed explanation-1: -The phylum echinoderms is divided into five extant classes: Asteroidea (sea stars), Ophiuroidea (brittle stars), Echinoidea (sea urchins and sand dollars), Crinoidea (sea lilies or feather stars), and Holothuroidea (sea cucumbers). The most well-known echinoderms are members of class Asteroidea, or sea stars.

Detailed explanation-2: -The echinoderms (Greek for spiny skin) include sea stars, sea urchins, feather stars, brittle stars and sea cucumbers.

Detailed explanation-3: -Introduction: Starfish, sand dollars, and sea urchins all belong to a group (phylum) of invertebrates known as echinoderms. The word “echinoderm” means spiny skin, which describes most of the organisms in this phylum.

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.