The Collaborative International Dictionary
Archaeostomatous
Archaeostomatous \Ar`ch[ae]*o*stom"a*tous\, a. [Gr. 'archai^os ancient + sto`ma mouth.] (Biol.) Applied to a gastrula when the blastopore does not entirely close up.
Wiktionary
archaeostomatous
a. (context biology English) (non-gloss definition: Applied to a gastrula when the blastopore does not entirely open up.)