Which of the following organisms does NOT belong to the Echinodermata phylum?

Echinodermata is a phylum that includes marine animals characterized by their radial symmetry and a unique water vascular system. This phylum encompasses several well-known classes, such as Asteroidea (sea stars), Ophiuroidea (brittle stars), Holothuroidea (sea cucumbers), and Echinoidea (sea urchins).

Coral reefs, however, are not part of the Echinodermata phylum; they are primarily made up of coral organisms, which belong to the phylum Cnidaria. Coral polyps are small, soft-bodied organisms that can secrete calcium carbonate, forming the hard structure of the reef. The distinction arises because Cnidarians differ significantly from echinoderms in terms of body structure, cellular organization, and reproductive strategies.

The other organisms listed—sea cucumbers, brittle stars, and sea urchins—are all members of the Echinodermata phylum, showcasing features like a calcareous endoskeleton, tube feet, and a pentamerous body plan in adult forms. Understanding this classification helps clarify the diversity within marine ecosystems and the significant role played by different organisms in these environments.