Class Anthozoa -> Subclass Hexacorallia -> Order Scleractinia
Stony Corals of the Order Scleractinia are the architects of the reef structure. Scleratinia have 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 antiquated view still serves as a guideline for care where SPS need more attention to detail than their LPS counterparts. The rationale is the average LPS coral is more tolerant to poor water quality than SPS. Also, SPS tend to need very intense light and flow compared to LPS.
As with any rule, there are a multitude of exceptions. For example, there is a world of difference between an Acropora and a Seriatopora when it comes to coral husbandry despite both being SPS. We encourage hobbyists to research each of the SPS corals to determine their individual care requirements.
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.