[], (Adjective)

Definitions:
- 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.


Phrases:

Origin:
mid 19th century; earliest use found in Louis Agassiz (1807–1873), zoologist and geologist. From ancient Greek ἀκτῖν-, ἀκτίς ray + -al