According to Mõtus and Y. Zaika (2012), the species which occurred in Rakvere was first described by Eichwald in 1854. Later two type specimens of the species from Rakvere were illustrated as Diplastraea diffluens by Eichwald (1860, fig. 11a-b). Bondarenko (1980)redescribed one specimen (fig. 11b) as Diplastraea diffluens. The other specimen turned out to be another taxon (Paramongoliolites spiralis). The first specimen was selected as the lectotype of D. diffluens by Bondarenko and Gataulina (1986), but that lectotype specimen is not preserved. The only thin section of the specimen was damaged in a fire. Only a small piece of it has survived. Therefore Mõtus and Y. Zaika (2012) designated a neotype for this species redescribing it as Protaraea diffluens (Eichwald, 1854).