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: -Final answer: Body symmetry in Echinodermata is radial.

Detailed explanation-3: -Echinoderms take many forms of symmetry. Pentameral symmetry is the major form and the other forms are derived from it. However, the ancestors of echinoderms, which originated from Cambrian period, were believed to be bilaterians. Echinoderm larvae are bilateral during their early development.

Detailed explanation-4: -Organisms belonging to the phylums Coelenterata, Echinodermata and Ctenophora exhibit radial symmetry.

Detailed explanation-5: -Radial symmetry is a form of symmetry in which identical parts are arranged in circular fashion around the central axis. Thus, cutting it through the central axis in any direction gives identical parts. Eg-Hydra, Obelia (Coelenterata), starfish etc.