actinaladj.
/akˈtʌɪnl/, /ˈaktɪnl/, U.S. /ækˈtaɪn(ə)l/, /ˈæktən(ə)l/ Zoology.
Designating the part or surface of an echinoderm or other radiate animal which contains the mouth and surrounding organs (as the lower or oral side of a starfish); relating to this part.Originally introduced in connection with Agassiz's theory that the body of a radiate animal is essentially a sphere, with the mouth or actinostome at one of the poles.
ΚΠ
1857 L. J. R. Agassiz Contrib. Nat. Hist. U.S.A. 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 J. D. Dana Corals & Coral Islands i. 22 The upper extremity (of an actinia) is called the actinal end, since it bears the tentacles or rays.
1946 H. Woods Palæontol. Invertebr. (ed. 8) 120 The under surface [of the asteroid] (known as the oral, ambulacral, or actinal, fig 54) is marked by the mouth, and the five deep ambulacral grooves.
2001 T. S. Hopkins & C. R. R. Ventura in M. Barker Echinoderms 2000 454/2 The development of the actinal groove.
Derivatives
acˈtinally adv. on or towards the actinal surface.
ΚΠ
1888 G. Rolleston & W. H. Jackson Forms Animal Life (ed. 2) 546 In Echnoidea..the pore shifts either actinally (to the left) or abactinally (to the right).
1972 Jrnl. Royal Soc. N.Z. 2 147 No pedicellariae present, either abactinally, marginally or actinally.
This entry has been updated (OED Third Edition, November 2010; most recently modified version published online December 2021).
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adj.1857