abactinal
/əˈbaktɪnəl/ /aˈbaktɪnəl/Zoology
adjective
Designating the part or surface of an echinoderm or other radiate animal that is furthest from the mouth (as the upper side of a starfish); relating to this part.
Origin
Mid 19th century; earliest use found in Louis Agassiz (1807–1873), zoologist and geologist. From ab- + actinal.