SPS are small polyp stony corals that grow small polyps on a calcareous skeleton. They can be found in a variety of unique colors, shapes and sizes, usually found as either plate like, or branching corals. All SPS corals have a hard or stony skeleton created by aragonite, and often formed into cup-shaped structures called corallites, and is covered by a thin layer of tissue called the coenosarc. The foot of the polyps then grow from the coenosarc on these colonial corals, or attached directly to the substrate connected by a pedal disc. SPS get all of there nutrients through a process known as photosynthesis, and will also feed on small meaty foods found in the water column, such as zooplankton. SPS are generally more difficult to keep, and are usually rated as expert-only coral.