Marasmianympha is a genus of moths of the grass moth family (Crambidae). It contains a single species, M. eupselias. Among the grass moths, it belongs to subfamily Spilomelinae. It is endemic to the Marquesas Islands of Polynesia, where it has been recorded on Fatu Hiva, Hiva Oa and Tahuata, but is suspected to occur on other islands as well. The holotype specimen is in the BMNH.