Description
Coral is a collective name for marine animals in the Anthozoa class. These are tiny creatures, only a few millimeters long, that, with their tentacles, resemble a sea anemone (see also Coelenterates). These creatures, also called polyps, often live in colonies. The brain coral in the photo is an example of such a colony. Coral colonies are often part of coral reefs. Within the Anthozoa class, we distinguish two subclasses: Alcyonaria and Zoantharia. Alcyonaria are also called Octocorallia, after the eight (octo) tentacles each polyp has. The corals in this group include soft corals: they do not produce an external calcareous skeleton. Zoantharia, or Hexacorallia, are polyps with six (hexa) tentacles or a multiple thereof. The corals that build coral reefs, limestone formations, belong to this group. Reef-building corals are colonial corals. The polyps from the colony collectively form a calcareous external skeleton. This occurs on top of the skeleton of deceased polyps from the same colony. This is how coral reefs grow slowly but surely. There are also solitary corals: they grow individually within their own calcareous external skeleton. Currently, approximately 4,500 species of coral are known. Locally, they form large colonies—banks and reefs, for example, the 2,300 km-long Great Barrier Reef off the coast of Australia. Corals grow in all warm and clean seas and oceans. In historical times, they were common in the Mediterranean Sea near Tunisia, Algeria, Italy, and the islands of Corsica, Sardinia, and Sicily. The red and orange-red forms still occur here, but to a lesser extent. Coral also grows in the Bay of Biscay. White corals are known from the Sea of Japan, salmon-red off the coast of Taiwan, pink corals grow near Midway Island in the Pacific Ocean, and black species grow near the Hawaiian Islands.
