Source : Webster's Revised Unabridged Dictionary (1913)

Trachymedusae \Tra`chy*me*du"s[ae]\, n. pl. [NL., fr.Gr. ? rough
   + medusa.] (Zo["o]l.)
   A division of acalephs in which the development is direct
   from the eggs, without a hydroid stage. Some of the species
   are parasitic on other medus[ae].