acraniate
/(ˌ)eɪˈkreɪnɪət/Zoology
adjective
Lacking a skull or cranium; (formerly) specifically belonging to the subphylum Cephalochordata (formerly Acrania) of primitive vertebrates lacking braincases.
noun
An acraniate organism; especially a cephalochordate.
Origin
Late 19th century; earliest use found in Canadian Journal. Either from a- + craniate, or from scientific Latin Acrania + -ate.