In biology, relating to the surface or part of an organism (especially a starfish) that is opposite from where the mouth is located.
From 'a-' (without, away from) plus 'actinal' (relating to the radius or ray-like structure). 'Actinal' comes from 'actinus' (a ray), so 'abactinal' literally means 'away from the rays.' The term is used in marine biology since the late 1800s.
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