Restoration of the morphology of Angustidontus seriatus Cooper, 1936 based on complete specimens from the Famennian of Nevada and Poland, supports its affinity to the coeval alleged decapod Palaeopalaemon and suggests eocarid (possibly also peracarid) affinities. Predatory adaptation of the thoracopods and the relatively short pereion make this crustacean only superficially resemble the archaeostomatopod hoplocarids, because the large grasping appendages of Angustidontus represent the first, rather than second, maxillipeds and acted in the opposite direction: downward. Another similar adaptation of the antennae in the Viséan Palaemysis suggests a widespread adaptation to predation among early eumalacostracans. The large sample collected from the Woodruff Formation of Nevada permits biometric characterisation of the grasping maxillipeds of Angustidontus, showing that their highly variable morphology should not be used to define species. All previously described species are therefore here synonymised with A. seriatus. Differences in gnathobases of mandibles found in articulated specimens in Nevada, and associated with isolated maxillipeds and articulated specimens possibly representing another unnamed species in Poland, suggest that such mandibles may eventually prove to be taxonomically more significant.