protostoma

Noun

protostoma (plural protostomata)

1. (obsolete) Synonym of blastopore.
   • It is frequently stated by critics of the protostoma hypothesis that it involves a reversal of dorsal and ventral sides during the evolution of Vertebrates from their invertebrate ancestors but it will be gathered from what has been said that this criticism rests on a misunderstanding.1919, Ernest William MacBride, Text-book of Embryology
   • 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, John Graham Kerr, Zoology for Medical Students, page 150

   Synonyms:

   blastopore

2. 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, Konstantin Ivanovich Skirabin, Key to Parasitic Nematodes, volume 1
   • Conventionally, the stoma is divided into three parts: the anterior chamber or cheilostoma, the middle or protostoma, and the posterior or telostoma.1977, Ivan Antonovich Rubtsov, Aquatic Mermithidae of the Fauna of the USSR