The Horn Coral Hydnophora, Hydnophora sp., is a SPS coral also known as fthe Knob Coral, Velvet Horn, and Branch Coral. They are often a deep luxuriant green hue varying in brightness. The Horn Coral Hydnophora can be encrusting meaning it grows upon positioned live rock, or branching reaching out into the aquarium. They have the ability to engorge their external tissue to give off the impression of a carpet-like or velvet texture. This species of coral comes in many shapes and sizes so it is difficult to show exactly what any given specimen will look like. Be careful not to place the Horn Coral Hydnophora near any other corals as there is a good possibility that it will kill nearby corals with its aggressive tentacles.