The echinoderms are
arborial insects
marine animals
terrestrial insects
freshwater forms
B.
marine animals
All members of Phylum- Echinodermata are marine. Therefore, Echinoderms are marine, spiny skinned animals. They have water vascular system for locomotion, eg, starfish, Antedon.
Arboreal insects lives on trees. Freshwater forms are animals or plants living in fresh water of ponds, eg, Hydrilla.