It occurs in the Indo-Pacific Ocean in areas with little wave action, favouring back reef environments from 3 to 20 m (10 to 66 ft) depth.

[4] In older specimens, particularly those exceeding 2 metres (6 ft 7 in) in diameter, the regular structure sometimes breaks down near the centre and there are growth anomalies.

One of these, Cymo melanodactylus, lives in association with Acropora cytherea but its low numbers (fewer than three per coral) mean that its host suffers little harm.

In the Chagos Archipelago these crabs have shown a change in their behaviour and have been found in large numbers infesting diseased and dying corals.

[1] One of the threats it faces is from the voracious crown-of-thorns starfish which has become more abundant in the Pacific and Indian Oceans since about 1970 and has periodical breakouts when its numbers increase dramatically.