Abstract
Light and electron microscope observations have been made of Opephora olsenii collected from brackish water sites mainly on the Swedish west coast, where it is one of the dominant species in the epipsammic microflora. O.olsenii differs from other taxa allocated to Opephora in having interlocking spines originating from a bar at the junction of valve face and mantle. O.olsenii is probably abundant in the benthos (especially the epipsammon) of brackish water areas around the world, but has previously been overlooked or misidentified.