good point Shagstah! I agree. A colony can fit on a plug if it has a tiny base.

Even more technically correct if the coral has several polyps it's a colony! haha:

http://en.wikipedia.org/wiki/Coral

A coral "head," which appears to be a single organism, is a colony of myriad genetically identical polyps. Each polyp is typically only a few millimeters in diameter. Over many generations the colony secretes a skeleton that is characteristic of the species. Individual heads grow by asexual reproduction of individual polyps."