Anterior part of the embryonic digestive tract that develops into a mouth. The stomodeum includes as parts an invagination of the ectoderm and the stomodeal cavity.
Comment:
[taxon-note] "This class groups together disparate structures as all being the anterior part of the early metazoan digestive tract and precursor of the mouth. However, the developmental processes vary, so this class may be split in future. E.g. in mammals it is a rostral depression surrounded by prominences. Outgrowth of the prominences produces a stomodeal cavity."