Few cnidarians like corals have a skeleton composed of

Cnidarians are aquatic, mostly marine, sessile or freeswimming, radially symmetrical animals. The presence of the stinging capsules or nematocytes is the characteristic feature of cnidarians and they are present on the tentacles and the body for anchorage, defense and for the capture of prey. Some of the cnidarians, e.g., corals have a skeleton composed of ${\mathrm{CaCO}}_3$.