[5] The colonies are bushy with small conical mounts called monticules that are unique because they form where the corallite walls of the adjacent polyp fuse together.

They are simultaneously hermaphrodite coral that develop eggs earlier than the testis and there are some strong indications that many colonies of H. rigida carry out multiple gametogenic cycles each year.

[6] In the Houtman Abrolhos Islands, the coral colonies would contain ripe eggs in March, so people inferred that they are part of the mass spawning event that happens in western Australia.

It has been found that the population of H. rigida was always in a fertile condition from November to February[6] and this indicates that the spawning season may spread over several months each year.

Then they begin to form tiny polyps that excrete calcium carbonate and slowly develop into a coral.