The Collaborative International Dictionary of English v.0.48:

Acerous \Ac"er*ous\, a.
   Same as Acerose.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Acerous \Ac"er*ous\, a. [Gr. [alpha] priv. + ke`ras a horn.]
   (Zool.)
   (a) Destitute of tentacles, as certain mollusks.
   (b) Without antenn[ae], as some insects.
       [1913 Webster]