Plectronoceratoidea is a superorder or subclass containing primitive nautiloids from the Late Cambrian and Early Ordovician.

[3] A few older studies consider Plectronocerida to be descended from Ellesmerocerida (rather than ancestral),[4] but this is no longer believed to be the case.

[6] Ordovician ellesmerocerids in turn likely gave rise to several new nautiloid superorders: Endoceratoidea, Multiceratoidea, and Orthoceratoidea.

The Ordovician-Triassic Orthoceratoids are ancestral to post-Paleozoic groups such as ammonoids (ammonites) and coeloids (modern cephalopods without external shells).

[3] Plectronoceratoids are generally small to tiny forms with orthoconic or endogastric shells, a few being exogastric, with proportionally large ventral siphuncles that contain numerous diaphragms.