Archaeodesmotraca (lit. "Old Desmostraca") was the earliest lineage of Desmostraca.
These early Desmostracans tended to be adaptable omnivores, feeding on Malacoformes and Caulophyte species and maintaining a relatively mobile lifestyle. Their banded shell allowed them to curl up into a ball as a defense mechanism.
Like the other two clades of Diplostoma, Desmostraca was negatively affected by the emergence of the Osteopods. In the case of Desmostraca, the Platydonts out-competed them for many of the adaptable omnivore niches: the Archeodesmostraca clade was driven to extinction, while the remaining Desmostracans evolved into the Eudesmostraca clade.