State the function of the water vascular system (tube feet) in echinoderms.

Write the general characteristics of the phylum Echinodermata.

Absence of excretory organs,high power of regeneration,and exclusively marine; these are the characteristics of the phylum:

The larval stage in Asterias is:
$(a)$ Absent
$(b)$ Free-swimming
$(c)$ Bilaterally symmetrical
$(d)$ Radially symmetrical

Which phylum consists of animals that are free-swimming in the larval stage and sessile (attached to a substrate) in the adult stage?

Echinoderms are headless,brainless,and heartless. Yet,they are placed at the top of invertebrates because of the presence of: