A new polycotylid plesiosaur from the early Turonian (Cretaceous) of the region of Goumima, Moroccom is described. The holotype ofManemergus anguirostris n. gen. et sp. comprises the subcomplete axial skeleton and partial appcndicular skeleton of an articulated juvenile individual. Owing to the young age of the specimen, the nature of anatomical variation during ontogeny in plesiosaurs is discussed. The new taxon is characterised by its skull architecture combining a narrow, relatively short rostrum and a box-like post-orbital segment, and smooth, slender teeth. The state of preservation hints at a relative in vivo stiffness of the neck due to strong intervertebral connections.