The Zoanthiniaria are a small group of polypoid anthozoans. They differ from most "sea anemones" (which are classified in the taxon Actinaria) in details of internal anatomy. Also, unlike most sea anemones, zoanthiniarians can form true colonies in which all members are connected by common tissue. This is visible in this colony of Palythoa from Mulegé, Baja California, México, in the Gulf of California. Palythoa is very common on low intertidal and subtidal rocks, where it is an important food source for mollusks such as cypraeid gastropods (cowries).
Zoanthiniarians make no hard parts and have no fossil record. However, they are more closely related to extinct coral taxa with an extensive fossil record -- the Tabulata and Rugosa -- than they are to other soft-bodied anthozoans.