Cancrion khanhensis sp. nov. (Crustacea: Isopoda: Entoniscidae) infesting Monomia haanii (Stimpson, 1858) (Crustacea: Brachyura: Portunidae) from Nha Trang Bay, Khanh Hoa, Vietnam, with remarks on larval stages of entoniscids and description of a new family, genus and two new species of hyperparasites infesting entoniscids.

An undescribed entoniscid isopod was found to parasitize Monomia haani, a common portunid crab in Khanh Hoa province of Vietnam. The new species is the eighth in the genus Cancrion, the second species of Cancrion found parasitizing hosts in the family Portunidae, and the first member of the family Entoniscidae to be described from southeast Asia. The cryptoniscius larva of a species of Cancrion is described for the first time. The new entoniscid infests hosts with a prevalence of 10.1% and intensity of 1 or 2 females per host. A new family, genus and species of cryptoniscoid hyperparasite with novel female and cryptoniscus body morphology is also described; this is the first record of a hyperparasite found infesting an entoniscid isopod. The purported cryptoniscus larva of Tiarinion texopallium Shields Ward, 1998 is shown to be that of a hyperparasitic cryptoniscoid isopod closely allied to the new Vietnamese hyperparasite and is described as a new species belonging to the new family and genus.