Descriptions of two new species of Megacepon George, 1947 from Chinese waters are presented. These two new species differ from the other four described species (and all other records of species in the genus) in having females with fusion in pleonal segments, in the shapes of the projections arising from pereomere 6 and pleomere 1, and in shape of oostegite 1. The varunid crabs Metaplax sheni Gordon, 1931 and Metaplax longipes Stimpson, 1858 are recorded as bopyrid hosts for the first time. A list of all records of Megacepon is provided, with remarks, in light of the possibility of cryptic species within the genus.