Diversity In Living Organisms — Science STD 9 — Question

1. Simple animals may be a star like, spherical or elongated.
2. Body is triploblastic, coelomate, unsegmented and radially symmetrical.
3. Body lacks head but has oral and aboral surfaces. Oral surface of the body has five radial areas called ambulacra.
4. Body wall is covered with spiny hard calcareous (calcium carbonate) plates (ossicles) that forms a rigid or flexible endoskeleton.

Example: Echinus (sea urchin) and Asterias (star fish).