[2] Cyrtocerinids can be characterized by a broad siphuncle encased by very thick connecting rings with concave outer surfaces.

Despite their thickness, the connecting rings are nautilosiphonate, meaning that their inner layer is a poorly-mineralized organic sheath (similar to modern nautiluses) rather than a porous calcified structure.

[1] The body chamber is oncomyarian, meaning that it is ringed by numerous small, undifferentiated muscle scars.

[4] Current studies generally consider Cyrtocerinida to be the earliest-branching monophyletic clade within the subclass (or superorder) Multiceratoidea.

This is justified by the combination of oncomyarian muscle scars, nautilosiphonate connecting rings, and endosiphuncular deposits.