Paratornoceratinae is a subfamily of oxyconic dimeroceratids

Dimeroceratidae

Dimeroceratidae is one of three families in the Dimeroceratoidea , a goniatid superfamily included in the Ammonoidea, which are extinct shelled cephalopods with a greater affinity to modern coleods than to shelled nautiliods....

 included in the order Goniatitida, a group of Paleozoic ammonoids, which have closer affinity to living coleoids

Coleoidea

Subclass Coleoidea, or Dibranchiata, is the grouping of cephalopods containing all the primarily soft-bodied creatures. Unlike its sister group Nautiloidea, whose members have a rigid outer shell for protection, the coleoids have at most an internal bone or shell that is used for buoyancy or support...

 than to Nautilus

Nautilus

Nautilus is the common name of marine creatures of cephalopod family Nautilidae, the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina. It comprises six living species in two genera, the type of which is the genus Nautilus...

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Paratornoceratinae as defined by Ebbighausen, Becker, & Bockwinkel in 2002 comprises three recognised genera with sharp, oxyconic, venters; Acrimeroceras

Acrimeroceras

Acrimeroceras is an oxyconic Devonian gonitite and one of three genera included in the subfamily Paratornoceratinae. The others being Paratornoceras and Paratoceras or ex Polonites....

, Paratornoceras, and Polonites. The shell, as described for the type, Paratornoceras, is subglobular and evolute on young stages, but discoidal and with closed umbilicus in the adult.