Common names include Bubble Coral, Bladder Coral, and Grape Coral and this is one of the more popular photosynthetic LPS corals. Specimens over 3 feet across have been seen in the wild. There are at least three species of bubble corals; the one mentioned below as named by (Dana in 1846), the quite rare Plerogyra simplex (Rehberg, 1892) and Physogyra lichtensteini (Milne Edwards & Haime, 1851) also rarely seen. They are all related to hammer, frogspawn, and elegance corals and are found throughout the Indo Pacific and in the Red Sea.
They come from a wide variety of environments, e.g., muddy and sandy bottom areas and attached to vertical walls. Their calcium carbonate skeleton usually forms a fattened oval or rounded shape. The more common bubble coral develops a somewhat flattened, yet continuous and unbranched wall of fused vertical plates (septa) with top area covered by the fleshy part of the animal.
The large multi-mouthed polyp is almost always extended with dime to quarter-sized water filled bubbles (vesicles) attached along its outer edge. Bubbles are usually .5 to 1.0 inch (1 - 2.5 cm), sometimes larger. Some bubbles appear to have a fingerprint pattern on their surface. At night, they retract and the coral displays long sweeper tentacles, sometimes 3 or 4 inches (7.5 - 10 cm) in length that can sting neighbors downstream that are within reach. It should be noted the short tentacles seen associated with the bubbles during the day do not contain nematocysts as does the sweepers extended during the night.
The most common color is tan, yet some species exhibit a pale green or pink tinge. Some light tan to almost white colored specimens probably received more light than darker brown specimens. Those with colored tints require slightly better lighting than brown or tan specimens. Generally, most prefer low light and do better with indirect light. Alkalinity should be kept in the 10 - 12 dKH range and phosphate, which interferes with calcium deposits, below .05 mg/l. Since the animal's septa are quite sharp, handling during collection and shipping can easily damage the skeleton or tissue material. It's always better to select a specimen that looks healthy and shows no signs of damage or tissue recession.
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