Coelogynopora schockaerti n. sp. (Proseriata: Coelogynoporidae) is described from the northwestern Gulf of Lion, Mediterranean. Only a few representatives of this genus are reported from Mediterranean marine sandy shores and only from the northwestern to central Mediterranean, but all of these species also occur outside the Mediterranean. So far, C. schockaerti n. sp. is the only species exclusively known from the Mediterranean. The species is solely encountered in the Gulf of Lion, a coldwater pocket in the Mediterranean and can, therefore, be considered as a remnant of an ancient coldwater platyhelminth fauna. C. schockaerti n. sp. is characterized by the shape and size of the spines of the male copulatory organ and the presence, orientation, shape and size of the two accessory spines. An identification key is given for the entire genus.