Melithaea sea fan, on a coral reef. Sea fans are also known as gorgonians. Each gorgonian polyp (too small to be seen here) feeds using tentacles which filter out plankton and particulate matter from the surrounding water. Also present are pygmy sweepers (Parapriacanthus ransonetti, lower left), a type of reef fish. Photographed in the Andaman Sea, off the Similan Islands, Thailand.