An evaluation of the notaspidean genera Pleurobranchopsis Verrill and Gymnotoplax Pilsbry (Opisthobranchia: Pleurobranchinae)

This paper presents a clarification of the status of two pleurobranch genera that have repeatedly been misunderstood and caused confusion. Since the holotype of Pleurobranchopsis aurantiaca Verrill 1900 ( = Pleurobranchus verrilli Thiele 1931) is apparently lost, there can be no certainty about its taxonomic position and the taxon should be treated as a nomen dubium. Examination of the holotype of Pleurobranchus americanus Verrill 1885 (type species of Gymnotoplax Pilsbry 1896 shows it to be a species of Berthella Blainville with the mantle mutilated to such a degree that the shell has been uncovered. It is doubted that any members of the Pleurobranchidae exist in the living state with partially or wholly uncovered shells.