Craspedota

Craspedota, a sub-class of the Hydrozoa (q.v.) including all those in which the medusa (or jellyfish, q.v.) has the mouth constricted by a flat broad ring known as the velum. It includes three orders, the Hydroidea, Trachymedusae, and Siphonophora. The first is the most important. Hydra (q.v.), the common fresh water polype, is its most typical member, but it also includes Cordylophora (q.v.), the Corynida (q.v.), the Hydrocorallina (q.v.), Campanularia, and the "Sea Firs." The Trachymedusae develop directly by metamorphosis from a free Hydroid larva. The Siphonophora includes the Portuguese Man of War (Physalia), Vellella, and other less known types. All the Craspedota are marine except Limnocodium (q.v.), a small form found in the Victoria regia tank at Kew, and one recently found in Tanganyika; this latter is an additional argument for the originally marine origin of those lakes.