Holothuroidea (sea cucumbers; phylum Echinodermata, subphylum Echinozoa) A class of worm-like echinoderms which may be free-living or attached. The mouth, surrounded by variably branched tentacles, is at one end of the elongate body, the anus at the other. The calcitic skeleton is not rigid, being reduced to small sclerites (or spicules) of very variable shape: hooks, anchors, rings, and plates. Fossil spicules of sea cucumbers are first encountered in rocks of Ordovician age.

Holothuroidea (holothuroids; sea cucumbers; subphylum Echinozoa) Class of worm-like echinoderms which may be free-living or attached. The mouth, surrounded by variably branched tentacles, is at one end of the elongate body, the anus at the other. The calcitic skeleton is not rigid, being reduced to small sclerites (or spicules) of very variable shape: hooks, anchors, rings, and plates. Fossil spicules of sea cucumbers are first encountered in rocks of Ordovician age.