Zoanthids belong to the same Subclass as stony corals and corallimorphs. They all have 6-fold symmetry in common and lack a calcium-based skeleton. 6-fold symmetry means the coral has six tentacles or tentacles in multiples of six. The distinguishing feature of this Order is the number of mesenteries and the distribution of perfect mesenteries. Zoanthids are a higly diverse Order with species colonizing both shallow and deep water.