If a polyp, such as Hydra, be regarded simply as a sessile actinula, we must certainly consider the polyp to be the older type, and it may be pointed out that in the Anthozoa only polyp-individuals occur.
Orders: Anthozoa and Cylicozoa.
By some authorities the Scyphomedusae have been removed from the Hydrozoa and united with the Anthozoa in a common group termed Scyphozoa.
At the parting of the ways which led, on the one hand, to modern Scyphomedusae, on the other to Anthozoa (III.), it is probable that the common ancestor was marked by incipient mesenteries and by the limitation of the sexual cells to endoderm.
For further details of colonyformation the reader is referred to the articles Anthozoa and Hydromedusae.
Hertwig.) The Anthozoa are divis ible into two sub-classes, sharply marked off from one another by definite anatomical characters.
To Anthozoa - this group abandoned its power of adult locomotion by swimming.
The Anthozoa differ from the Scyphomedusae in having no medusoid form; they all more or less resemble a sea-anemone, and may be termed actinioid.