The lowest selection of Vertebrata, including the amphioxus, which no skull is present.
[NL., fem. sing.] In teratology, a malformation consisting in a whole absence of the bones and integuments developing the vault for the skull. In addition written acrany.
[capitalized] [NL., neut. pl.] A name recommended by Haeckel as a class designation for Amphioxus or Branchiostoma; a synonym of Myelozoa or Leptocardia (which see). Also known as Acephala. See Amphioxus and Branchiostoma.