The Collaborative International Dictionary of English v.0.48:

Dicyemata \Di`cy*e"ma*ta\, n. pl. [NL., fr. Gr. di- = di`s-
   twice + ? an embryo.] (Zool.)
   An order of worms parasitic in cephalopods. They are
   remarkable for the extreme simplicity of their structure. The
   embryo exists in two forms.
   [1913 Webster]