Genera: (a) Ore supero; basi se affigens: Actinia, Ascidia.
The most familiar Anthozoan is the common sea-anemone, Actinia equina, L., and it will serve, although it does not form a skeleton or corallum, as a good example of the structure of a typical Anthozoan polyp or zooid.
The individual animal or zooid of Actinia equina has the form of a column fixed by one extremity, called the base, to a rock or other object, and bearing at the opposite extremity a crown of tentacles.
In Actinia and its allies, and most generally, though not invariably, in Anthozoa,the stomodaeum is not circular, but is compressed from side to side so as to be oval or slit-like in transverse section.
In Actinia, as in all Anthozoan zooids, the coelenteron is not a simple cavity, as in a Hydroid, but is divided by a number of radial folds or curtains of soft tissue into a corresponding number of radial chambers.