The Collaborative International Dictionary of English v.0.48:

Otocyst \O"to*cyst\, n. [Oto- + cyst.] (Zool. & Anat.)
   An auditory cyst or vesicle; one of the simple auditory
   organs of many invertebrates, containing a fluid and
   otoliths; also, the embryonic vesicle from which the parts of
   the internal ear of vertebrates are developed.
   [1913 Webster]