Gymnoblastic Hydroids, an order of the Hydromedusse, a sub-class of the Hydrozoa (q.v.). The polyps form branching colonies, which are invested with a delicate chitinous cuticle, which does not, however, form cup-like expansions into which the hydranths can be withdrawn. Examples of the group are Tubularia, Cordylophora, Hydractinia. When free-swimming medusee are formed they possess eyes, and bear the sexual products round the manubrium; they are known as Anthomedusee (q.v.).