Answer: Colonial hydrozoans include siphonophore colonies, Hydractinia, Obelia, and many others. In hydrozoan species with both polyp and medusa generations, the medusa stage is the sexually reproductive phase. Medusae of these species of Hydrozoa are known as "hydromedusae".
Explanation: Because its Colonial hydrozoans include siphonophore colonies, Hydractinia, Obelia, and many others. In hydrozoan species with both polyp and medusa generations, the medusa stage is the sexually reproductive phase. Medusae of these species of Hydrozoa are known as "hydromedusae".