The Collaborative International Dictionary of English v.0.48:

Scyphistoma \Scy*phis"to*ma\, n.; pl. Scyphistomata,
   Scyphistomae. [NL., fr. Gr. sky`fos a cup + sto`ma the
   mouth.] (Zool.)
   The young attached larva of Discophora in the stage when it
   resembles a hydroid, or actinian.
   [1913 Webster]