Corals (Kingdom Animalia, Phylum Cnidaria, Class Anthozoa) are marine creatures. They’re essentially colonies of sea anemones that make a skeleton, usually mineralized. The hard skeleton is relatively easy to preserve, so corals are well represented in the fossil record. During the Paleozoic, common coral groups included the tabulates, the rugosans, and the heliolitids. All of these groups went extinct at the end-Permian mass extinction. Post-Paleozoic and living corals are all representatives of one group - the scleractinians. A lesser known group of corals is the octocorals (a.k.a. alcyonarians), known from the Cambrian to today.
Corallium rubrum (Linnaeus, 1758) - the red coral (a.k.a. precious coral, noble coral) is a spectacular example of modern octocoral. Polished fragments have been used as organic gemstones. The skeleton is aragonite (CaCO3) mixed with reddish-colored organic compounds. Corallium rubrum occurs in the northeastern Atlantic Ocean and the Mediterranean Sea. (public display, Field Museum of Natural History, Chicago, Illinois, USA)
Classification: Animalia, Cnidaria, Anthozoa, Octocorallia, Gorgonacea, Corallidae