Furthermore, common hermatype species such as the common Red Sea coral, Stylophora pistillata, which in shallow waters may be an important element in the reef structure, do not form reefs towards the lower limit of their distribution.
Such marine formations consist of the cemented skeletons of living organisms, known as hermatypes (reef-forming) and their dead remains.
However, these reefs were built by different hermatypes from those we are familiar with in present-day coral reefs.
Today, although some coral species are found outside the described boundaries, they are not hermatypes since they survive and grow as isolated colonies that never develop into continuous, stable reef structures.
The Octocorallians as a group, unlike the Hexacorallians, do not have calcium carbonate skeletons and, with few exceptions, are not hermatypes.
The various soft corals compete with Hexacorallians and other hermatypes for suitable substrates for settling.