Ctenella chagius is a massive, hemispherical, colonial coral with a fissured surface and brain-like appearance.

The fine septa that radiate from the corallites are closely packed and evenly spaced, some continuing upwards and over the ridges.

[4] This coral is a pale brown colour and can grow to a metre (yard) in diameter.

It is a zooxanthellate coral and has symbiotic unicellular dinoflagellate algae living within its tissues.

The size of its population is unknown but the reefs on which it lives are being degraded at a faster rate than it is likely to be able to establish new colonies.