Orthomorpha coarctata, the long-flange millipede,[1] is a widely introduced species of Polydesmidan millipede of the family Paradoxosomatidae.

It is presumed native to Southeast Asia but due to transport by humans occurs in tropical and sub-tropical areas throughout the world, including the Hawaiian Islands, the West Indies, Gulf Coast of North America, and the Galápagos Islands.

[4] O. coarctata can be distinguished from Oxidus gracilis, another widely introduced Asian millipede, by having proportionally longer and pointier paranota (lateral keels) on mid-body segments and longer gonopods (male reproductive appendages).

[5] O. coarctata is unique within the genus Orthomorpha in that the gonopods have a single, simple tip, while other species have two or three lobes.

This distinction has led some authors to place O. coarctata in a separate, monotypic genus, Asiomorpha.