is a specific kind of: invertebrate.

is a broader term that covers: sea star, starfish | brittle-star, brittle star, serpent star | basket fish, basket star | sea urchin | crinoid | holothurian, sea cucumber.

has as a part: water vascular system | ambulacrum | tube foot.

is a member of: Echinodermata, phylum Echinodermata.