Fifteen transverse rows of cerata on each side conceal most of the notum. Pale anterior row resembles the ruff on A. alderi but it is smaller, and close inspection shows that less than half of each ceras is occupied distally by a pure white cnidosac (1) and the rest is occupied by pale pink, possibly empty, digestive gland (2).
Translucent white head reveals internal, opaque white jaw (3) and buccal mass (4). Right eye visible; left eye hidden by the tilt of a rhinophore.
Length 20 mm. Menai Strait, Wales, July 2013.