invertebrate - any animal lacking a backbone or notochord; the term is not used as a scientific classification

water vascular system - system of fluid-filled tubes used by echinoderms in locomotion and feeding and respiration

Echinodermata, phylum Echinodermata - radially symmetrical marine invertebrates including e.g. starfish and sea urchins and sea cucumbers

ambulacrum - one of the five areas on the undersurface of an echinoderm on which the tube feet are located

sea star, starfish - echinoderms characterized by five arms extending from a central disk

brittle star, brittle-star, serpent star - an animal resembling a starfish with fragile whiplike arms radiating from a small central disc

basket fish, basket star - any starfish-like animal of the genera Euryale or Astrophyton or Gorgonocephalus having slender complexly branched interlacing arms radiating from a central disc

sea urchin - shallow-water echinoderms having soft bodies enclosed in thin spiny globular shells

crinoid - primitive echinoderms having five or more feathery arms radiating from a central disk

holothurian, sea cucumber - echinoderm having a flexible sausage-shaped body, tentacles surrounding the mouth and tube feet; free-living mud feeders: sea cucumbers

tube foot - tentacular tubular process of most echinoderms (starfish and sea urchins and holothurians) having a sucker at the end and used for e.g. locomotion and respiration