The examination of a collection of benthic macroinvertebrates from the Gulf of Thailand led to the erection of two new species of cumaceans (Crustacea), namely Pseudosympodomma carinatum sp. nov. (Vaunthompsoniinae, Bodotriidae) and Paradiastylis capillata sp. nov. (Diastylidae). Among the four species of the genus Pseudosympodomma, P. carinatum sp. nov. is related to P. indicum by having the first uropodal endopod article shorter than the second, but differs from it in lacking spines on the articles of the third maxilliped, as well as in having a high number of setae on the mandible and a more developed median carina on pedigerous somites two to four. The genus Paradiastylis is characterized by the absence of an exopod on the third maxilliped of females. Among the species of the genus, P. capillata sp. nov. is related to P. bathyalis by lacking folds in the carapace and having a long telson with a cylindrical pre-anal part. However, the two species may be differentiated by the relative length of the uropod endopod (longer than the exopod in P. capillata) and the basis of the third maxilliped (non-distally produced in P. bathyalis)