Mediterranean adults with a developed labial varix seem to have less crowded, less randomly arranged, opaque, white spots on their translucent white cephalic tentacles than those in Orkney. The dots may almost form two distinct lines.
LEFT: Shell height 8mm. Mediterranean form. Sublittoral. Novigrad, Croatia. November 2017. Leg. © A. Petani. RIGHT: Shell height 9.2mm. Atlantic form. Littoral, LWS. Orkney, Scotland. May 2017.