GENERAL HISTOLOGY

Detailed explanation-1: -The echinoderms have a radially arranged, pentamerous body structure that is very different from the bilateral body structure of the related deuterostome phyla, the hemichordates and the chordates. Yet, all three phyla evolved from a common bilaterally symmetric ancestor (Eernisse & Peterson 2004; Smith et al. 2004).

Detailed explanation-2: -Radial symmetry is found in the cnidarians (including jellyfish, sea anemones, and coral) and echinoderms (such as sea urchins, brittle stars, and sea stars).

Detailed explanation-3: -One characteristic of an echinoderm is that they all have pentamerous radial symmetry. This simply means they all have 5 equal body parts. You can divide these animals into five equal parts, and every part is the same. For example, most sea stars have five arms or a multiple of five arms.