Oerstedia dorsalis (Abildgaard, 1806)

Length usually 1–1.5 cm, occasionally 3 cm, width 1–2 mm. Head rounded but not narrow and not demarcated from body. Four dark eyes arranged in a square, body stout and cylindrical. Colour is very variable from dark brown to marbled, spotted or striped in different brownish nuances. Widespread in northern hemisphere, can be found from the surface and down in algal mats, gravel or shelly sediments. Can be mistaken for Oerstedia striata.