The tabulate and rugose ('wrinkly') corals shown on the previous pages did not survive the major end-of-
Permian mass extinction event. All post- Triassic corals, such as those shown on these two pages, and
including living types, are known as scleractinians. They superficially resemble rugose corals, but they
can be distinguished by their internal ribs, or septa, which are always arranged in multiples of six.