Interesting fun facts on the bubble coral Plerogyra sp. from Animal World.
" Species Description:
The Plerogyra genus, whether branching or not has a typical lightweight skeletal structure that is easy to cut or sever. The coral’s 1/2” to 1” (1 - 2.5 cm) polyp bubbles are oval and water filled, with a higher density of zooxanthellae than most symbiotic corals that have been studied to date. The bubbles will expand or contract as needed for acquiring more or less light. At night, they deflate and 3-4” (7.5 to 10 cm) feeder tentacles, which CAN sting, emerge looking for food. The small short tentacles seen with the bubbles during the day do not sting. The coral comes in shades of bluish green to green, cream and tan with lighter striations on the surface, but will turn brown if the light is too high. There are usually pieces of sharp, delicate, thin “bone” called septa in-between the bubbles. The tissue of the Plerogyra genus will actually connect and encrust onto nearby substrate. P. discus looks almost identical to the Fox Coral (Nemenzophyllia turbida) except each puffy polyp is connected to a separate branch, with the same flowery look. P. simplex (Branching Bubble Coral) has a similar look as P. sinuosa, except it has individual branches. These little groupings barely touch each other and are separated with quite a bit of space within the colony. P. sinuosa (Bubble Coral) comes in one colony with large water filled “bubbles” in a display that is easily recognizable. The “octobubble” term comes from the bubbles on some morphs being “nippled” at the tip. Some colonies can reach 3 feet (1 m) in the wild, but most are smaller, only getting to around 7.5” (19 cm). Lifespan is unknown."