A basal grade of Neognathostomata with:
Middle to Upper Jurassic (Bajocian-Kimmeridgian); Europe, Middle East, probably more widely distributed.
|Classification and/or Status||Irregularia, Microstomata, Neognathostomata stem group
Probably a paraphyletic grade.
Basal Microstomata that were previously placed in both the families Clypeidae Lambert, 1898 and Nucleolitidae Agassiz & Desor, 1847 and which have their periproct either still enclosed by the apical disc plates, or at least remaining in contact with the posterior ocular plates. Phylogenetic analysis (Barras, 2007) suggests that this may be a grade taxon.