What is "abactinal"

Abactinal \Ab*ac"ti*nal\ ([a^]b*[a^]k"t[i^]*nal), a. [L. ab + E. actinal.] (Zo["o]l.) Pertaining to the surface or end opposite to the mouth in a radiate animal; -- opposed to actinal. ``The aboral or abactinal area.''
--L. Agassiz.

a. (context zoology English) Pertaining to the surface or end opposite to the mouth in a radiate animal.

adj : (of radiate animals) located on the surface or end opposite to that on which the mouth is situated [ant: actinal]