The
Nautilida constitute a large and diverse order of generally coiled nautiloid cephalopods that began in the mid
Paleozoic and continues to the present with a single family, the
Nautilidae which includes two genera,
Nautilus and
Allonautilus, with six species. All told, between 22 and 34 families and 165 to 184 genera have been recognised, making this the largest order of the subclass
Nautiloidea.