Left: adapted from Plate 19, Family 1, in Alder & Hancock (1845 – 1855). The drawing shows the structure of the gills in a circle with a small gap at the rear and the anal papilla at the centre.
Right: the structure of the gills is often difficult to see in photographs because of their swollen nature and less than full extension. The cylindrical anal papilla (1) is at the centre of the gill circle.
ELWS, Menai Strait, Wales. 2011.