Class Anthozoa -> Subclass Hexacorallia -> Order Scleractinia
Stony Corals of the Order Scleractinia are the architects of the reef structure. Scleratinia are characterized by having 6-fold symmetry as well as a calcium-based skeleton. 6-fold symmetry means the coral has six tentacles or tentacles in multiples of six.
The reef aquarium hobby long ago divided stony corals into two categories, Large Polyp Stony (LPS) and Small Polyp Stony (SPS). This view is somewhat antiquated, but still serves as a guideline for care where SPS are thought to require more "expert care" than their LPS counterparts. The thinking behind this is on the whole LPS are more tolerant to water quality than SPS and SPS tend to require very intense light and flow. As with any rule, there are a multitude of exceptions so we encourage reef hobbyists to research each of the SPS corals individually to determine their care requirements. For example, there is a world of difference between an Acropora and a Seriatopora when it comes to coral husbandry.
Small Polyp Stony (SPS) Corals are the builders of calcium carbonate reef structures found in the wild. The skeleton of these corals is slowly secreted by the epidermis at the base of each coral polyp. The rate that this occurs depends on the species. Some varieties of SPS corals can grow very quickly while some other varieties take seemingly forever to show any growth. Stony Corals benefit from clean water and a consistent source of calcium, alkalinity, and magnesium.