Any of various cnidarians of the class Hydrozoa, including the hydras, hydroids, and siphonophores, which exhibit alternation of generations between the polyp and medusa stage or exist in only one or the other stage.
Of a class (Hydrozoa) of cnidarians having a saclike body consisting of two layers of cells, and a mouth that opens directly into the body cavity.
Any animal of this class, as a hydroid or Portuguese man-of-war.
Origin of hydrozoan
- From New Latin Hydrozōa class name Hydra type genus hydra -zōa pl. of -zōon -zoon
From American Heritage Dictionary of the English Language, 5th Edition