Class Anthozoa -> Subclass Hexacorallia -> Order Zoanthidia 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. An interesting behavior of zoanthids and palythoa is their uptake of debris into their flesh. Over time these polyps take on a speckled appearance particularly in and around their stalk and base.
The marketplace for Zoanthids over time has produced some rather colorful names for different morphs. While some may seem silly and over-the-top, I personally have warmed up to them. There are certainly discrepencies where a single zoanthid may have several "made up" names, but overall I find it helpful distinguishing the different color morphs. If someone were to ask about a red zoanthid with a blue ring and red mouth, there are many corals that spring to mind. If someone were to ask about a "Bam Bam Orange" I know what it is (ironically, a Bam Bam Orange has no orange in it IMO).