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The Helcionellacea includes two families according to the Treatise,1960, the Helcionellidae, which is the more primitive, and the Coreospiridae, which is the more derived.
Intejocerida is the name given to a group of generally straight shelled nautiloid cephalopods originally found in Lower and Middle Ordovician sediments in the Angara River basin in Russia; defined in the Treatise as an order, and combined there with the Endocerida in the Endoceratoidea.