What is the main distinctive feature of echinoderms?

Step-by-step solution

These animals have an endoskeleton of calcareous ossicles and, hence, the name Echinodermata (Spiny bodied, All are marine with organ-system level of organisation. The adult echinoderms are radially symmetrical but larvae are bilaterally symmetrical. They are triploblastic and coelomate animals. Digestive system is complete with mouth on the lower (ventral) side and anus on the upper (dorsal) side. An excretory system is absent. Sexes are separate. Reproduction is sexual. Fertilisation is usually external. Developm