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Soft corals and gorgonians

These animals (subclass Alcyonaria) are among the loveliest of the cnidarians. In the clean, plankton-rich waters of Indonesia, soft corals and gorgonians— sea whips or sea fans—are common. Some contain zooxanthellae, but many frequent the deeper parts of the reef, where they filter plankton from the water. Semi-precious pink "coral" is a gorgonian (Corallium), harvested from deep waters off Japan and in the Mediterranean.

Soft corals. Soft corals, as the name suggests, lack the hard limestone skeletons of their reef-building relatives. Instead, the numerous polyps that make up the colony are supported by a fleshy central "body"; in some cases strengthened by spicules, spines of silica or calcium.

Soft corals (order Alcyonacea) have few obvious defense mechanisms, and might seem to be vulnerable to attack by predators and parasites, or to fouling by overgrowth. The animals avoid these problems by secreting various bioactive substances, a kind of chemical defense. Substantial efforts are being made by biochemists and pharmaceutical companies to identify compounds in soft corals—and also sponges—that may have properties useful in medicine. Since many of these compounds have evolved to prevent alien growths, they are receiving attention as potential anti-cancer drugs.