The largest anemone on the reef and the one that sits in plain view: a disc reaching a metre (39 in) draped over the top of a coral head, with a column beneath it coloured blue, green, red or purple. Where other species hide the body and show only tentacles, this one is all body, and a big individual is visible from many metres away.
It takes exposed, current-swept positions on reef tops, which suits an animal that feeds on plankton and relies on symbiotic algae for much of its energy. Several clownfish species use it, and a large anemone commonly carries a whole family group plus damselfishes and shrimp. When disturbed it can pull the entire crown inward and become a coloured ball in seconds. The species has just been moved out of Heteractis into the genus Radianthus, so most books and dive guides still list it under the old name - both refer to the same animal.
- very large disc, often a metre across, sitting fully in the open
- column brightly coloured - blue, green, red or purple
- long tentacles with slightly swollen tips, evenly spread
- column visible below the crown, not hidden in a crevice
