Unlike most other hard corals which are colonies of tiny polyps, most mushroom hard corals are a single polyp.
A mushroom hard coral grows to about 10-15cm, sometimes longer. Considering that most hard coral polyps are tiny (0.5cm or less), mushroom hard corals are truly giants among polyps.
Not only that, they are also not attached to the sea bottom and can move about. You can almost hear them growl as they lurch around other tiny coral polyps stuck in their colonial skeletons!
What are mushroom hard corals?
Mushroom hard corals belong to the Family Fungiidae. They are solitary corals that are free-living (i.e., lie unattached on the ground) as adults.
Some mushroom hard corals have a circular disk-like skeleton.
The slit-like mouth of this solitary polyp is in the centre on the upper surface. The 'lips' are usually striped.
Others are long and tongue-shaped. An unidentified mushroom coral that is sometimes seen on undisturbed reefs.
Some mushroom corals, like Herpolitha sp. have Y- or X-shapes. This is generally due to regeneration following damage.
Some have really short tentacles!
This is Polyphyllia talpina which is listed among the threatened animals of Singapore.
Most have short tentacles, except for Heliofungia actiniformis that has such long tentacles that it is often mistaken for a sea anemone.Young mushroom hard corals start life attached to a surface, and look like tiny stalked mushrooms. In many species, as the coral matures eventually breaks away from the stalk and lives life as an adult unattached to the bottom.
Free-living mushroom hard corals can move! Though very slowly. And smaller ones can right themselves should they be accidentally overturned.
Some species of hard corals from other families are also giant polyps that lie unattached to the surface. This includes Trachyphyllia geoffroyi, a rather rarely encountered coral.
This beautiful coral is sometimes called the Banana coral because when its tissues are inflated underwater, these resemble bananas.
More photos of Singapore's mushroom hard corals on wildsingapore flickr.