a. Zool. [f. Gr. ἀκτίς, ἀκτῖν-α ray + -AL 1.] Pertaining to that part or surface of a radiate animal that contains the mouth and surrounding organs, as the lower side of a starfish; a term introduced by L. Agassiz in connection with his view that the body of a Radiate animal is essentially a sphere, with the mouth or actinostome at one of the poles.
1857. L. Agassiz, Contrib. Nat. Hist. N. Amer., IV. 376. The so-called mouth is always placed at one of these poles, and from it radiate the most prominent organs, in consequence of which I have called this side of the body the oral or actinal area, and the opposite side the aboral or abactinal area.
1872. Dana, Corals, i. 22. The upper extremity (of an actinia) is called the actinal end, since it bears the tentacles or rays.
