The Collaborative International Dictionary of English v.0.48:

Spermatoon \Sper`ma*to"on\, n.; pl. Spermatoa. [NL., fr. Gr.
   spe`rma, -atos, seed + ??? an egg.] (Anat.)
   A spermoblast. -- Sper`ma*to"al, a. --Owen.
   [1913 Webster]