BEWARE OF THESE. They have stinging polyps. Fire Corals are not true corals. They are a cnidarian but build a skeletal mass like stony corals do. They have a smooth appearance because they lack the coral polyp cups of true corals. Instead, they have pin-hole size apertures consisting of two types. A central hole for the feeding polyps, which sting their prey to paralyze them. The central hole is surrounded by other holes occupied by the defensive stinging polyps. They are fast growing and are a very important reef building organism.