Cucullanus diagrammae is a species of parasitic nematodes.

[1] It is an endoparasite of a fish, the Painted sweetlips Diagramma pictum (Haemulidae, Perciformes).

The species has been described in 2020 by František Moravec & Jean-Lou Justine from material collected off New Caledonia in the South Pacific Ocean.

[1]