acrania

1 of 2

noun

acra·​nia (ˈ)ā-ˈkrā-nē-ə 

: congenital partial or total absence of the skull

Acrania

2 of 2

noun plural

in some classifications

: a division of the phylum or subkingdom Chordata comprising the hemichordates, tunicates, and lancelets and including all the chordates without true heads and anterior brains compare vertebrata