; class Anthozoa, subclass Zoantharia)
An order of colonial (or, more rarely, solitary) corals, which always possess an external ectodermal, calcareous skeleton consisting essentially of radial septa. Septa develop following the pattern of mesenteries in cycles of 6, 12, 24, 48, etc. The order first appeared in the Middle Triassic.
Subjects: Zoology and Animal Sciences.