Black and orange marked forms of Polycera quadrilineata (left) & P. norvegica (right). 1: oral veil with four to six yellow elongate processes. 2: no sheath enclosing rhinophores. 3: large, translucent white, yellow- or orange-tipped (usually), erect lobe on either side of gills. Length 20 mm, Menai Strait, Wales, March 2010 and south-east Scotland, August 2012, © J. Anderson.