The brown form of Acanthodoris pilosa is sometimes confused with O. bilamellata but the brown is evenly distributed and does not form a distinct dorsal panel. It is further distinguished by soft, tall, slender, conical tubercles and by its tripinnate gills which, when expanded, form a large rosette, often wider than the body, with white pigment resembling a star.
Length 11 mm. Menai Strait, Wales. March 2015.