protostoma

noun2

1. •
   In nematodes, a particular division of the stoma (mouthlike opening).

   • The protostoma with its wall—the protorhabdion—is the major part of the stoma. — 1968
2. •
   (no longer used) Synonym of blastopore.

   • The opening of this, the protostoma, becomes elongated, taking on an elliptical shape, and then it narrows in the middle, its outline becoming that of a dumb-bell. — 1921