The Encrusting Horn Coral is a SPS coral often referred to as Knob, Velvet Horn, or Branch Coral. The most common form is green with darker green polyps, but less commonly will be cream in coloration with neon green polyps. This species is encrusting, and will grow over the adjacent rockwork. This species may also develop horn-like branches, reaching out into the water column. Hydnophora sp. corals have the ability to swell their tissue, giving the coral an inflated and fuzzy appearance.