mi·ra·cid·i·um 
(mîr′ə-sĭdē-əm, mī′rə-)
(mîr′ə-sĭdē-əm, mī′rə-)n. pl. mi·ra·cid·i·a (-ē-ə)
A ciliated larva of a digenetic trematode, which hatches from the egg and enters the first intermediate host, where it develops into a sporocyst or a redia.
[German, from Greek *meirakidion (attested in Latin as mīracidion, one in early adolescence), diminutive of meirax, young girl, young person, lad.]
mi′ra·cidi·al adj.