Also found in: Dictionary, Medical, Wikipedia.
(1) A genus of the Rhynchocephalia family of snake-necked tortoises. It is characterized by a very long neck (which exceeds the length of the dorsal shell) and by the presence of four claws on each of the front legs. The length of the carapace does not exceed 30 cm. There are two species, both freshwater and native to South America. Hy-dromedusa lays its eggs on the shores of inland bodies of water.
(2) Medusoid individuals of certain coelenterates of class Hydrozoa.