Two new species of the parasitic isopod genus Gigantione Kossmann, 1881 are described infesting the goneplacid crab Notonyx musuppocenta Clark & Ng, 2011. The new species (G. tuberculata and G. notonyxae) can be distinguished from other described species by their males having mid-ventral projections on the first three pleomeres. Gigantione tuberculata differs from G. rhombos An, Yu & Markham, 2009, G. tau, An, Yu & Markham, 2009, and G. giardi Nobili, 1906 in characters of the barbula, shape of the head of the female and uropods and antennae of the male. Females of G. notonyxae differ from G. pratti Danforth, 1967 in the dorsolateral bosses, oostegite 1 and coxal plates. In addition, females of G. notonyxae differ from those of G. tuberculata in possessing smooth coxal and lateral plates.This is the first report of N. musuppocenta bearing any parasitic isopods. The hosts and localities of 18 species of Gigantione are summarized and a key to the species is provided.