perienteron

from The Century Dictionary.

• noun The primitive perivisceral cavity persisting as a modified blastocœle after a blastosphere has undergone gastrulation; the blastocœle of a gasturla, or the space between the endoderm and the ectoderm, as distinguished from the cavity of the archenteron inclosed within the endoderm.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Anat.) The primitive perivisceral cavity.