In which class of Echinodermata is a stalk found for attachment to the substratum?

Which organ system is lacking in the animals that bear a water vascular system?

Cephalization is absent in

Which of the following is a characteristic of Phylum $Echinodermata$?

Assertion : Ambulacral system plays a major role in locomotion of echinoderm.
Reason : Hydraulic pressure of fluid and contraction of muscle of tube feet make possible movement of echinoderm.

Echinodermata is a group of animals which are