Gymnophthalmata \Gym`noph*thal"ma*ta\, n. pl. [NL., fr. Gr. gymno`s naked + ? the eye.] (Zo["o]l.) A group of acalephs, including the naked-eyed medus[ae]; the hydromedus[ae]. Most of them are known to be the free-swimming progeny (gonophores) of hydroids.