Appearance
Colonies of Plerogyra sinuosa are in the form of an inverted cone that may be as much as a metre (yard) across. The corallites in small colonies are monocentric and trochoid, but become flabellomeandroiid (arranged in valleys, the neighbouring valleys having separate walls) in larger colonies. The septa have smooth margins and are irregularly arranged. The costae on young colonies sometimes form lobes which develop spines. These spines then elongate and a new polyp develops, this budding method being an unusual occurrence among corals.
In the living coral, Plerogyra sinuosa has vesicles resembling bubbles up to 2.5 cm (1 in) in diameter. These enlarge during the day but retract to a certain extent during the night to expose the polyps and their tentacles.

