We describe here Haploginglymus morenoi n.sp. (Amphipoda Gammaridea Niphargidae) from the freshwater interstitial environment along Rio Mataraña, Beceite (Aragón), North-Eastern Spain. Sediment in the type locality is very fine-grained. Peculiar to the new species is article 6 of the maxilliped palp, which is spoon-like, with finely ciliated distal margin, rather than having the usual shape as a dactylus provided with a claw. Further diagnostic characters are provided by the sexually dimorphic gnathopods II and by the very elongated dactylus of pereiopods 6 and 7, whose claw is extremely short. One of the specimens of the type series is anomalous, in that its maxilliped has a pretty normal left dactylus, the right one being however shaped as in the other specimens of this species.