The Collaborative International Dictionary of English v.0.48:

Rhizocephala \Rhi`zo*ceph"a*la\, n. pl. [NL., fr. Gr. ??? root +
   ??? head.] (Zool.)
   A division of Pectostraca including saclike parasites of
   Crustacea. They adhere by rootlike extensions of the head.
   See Illusration in Appendix.
   [1913 Webster]