SPS corals are an order of coral species that have a stony calcium carbonate skeleton with tiny coral polyps. SPS, referring to their stony structure (which makes them hard corals) as ‘small polyp stony’ are in the class Scleractinia and the phylum Cnidaria. Examples include: Montipora and Acropora (branching and plating), seriatopora, pocillapora and much more!