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: -Adult echinoderms have radial symmetry, but larvae have bilateral symmetry. Echinoderms have a unique water vascular system, with canals that extend along each body part.

Detailed explanation-3: -Only a few animal groups display radial symmetry, while asymmetry is a unique feature of phyla Porifera (sponges). All types of symmetry are well suited to meet the unique demands of a particular animal’s lifestyle.

Detailed explanation-4: -Sea stars are related to sand dollars, sea urchins, and sea cucumbers, all of which are echinoderms, meaning that they have five-point radial symmetry.