Size: Up to about 60mm long - Britain's largest chiton. Shape: Very broad girdle with the shell making up 30-40% of the width. Valves are relatively tall and rounded, but still with a definite keel. Shell colour: variable though generally pale with mottled or streaked combinations of white, yellow, brown, black or green; the keel often contrasts with rest of valve. Sculpture: Valves have crowded, minute, circular, evenly distributed granules, except on dorsal keel which has longitudinally arranged ridges and grooves Girdle: Has 18 conspicuous tufts of bristles up to about 2mm in length. The girdle is variable in colour including white, yellow, ochre, pink and magenta. Animal: Gills confined to the latter half of the animal (merobranch).
The eight valves are relatively strong and include notches on the areas where the valves embed in the girdle; five notches in the head valve and two in each of the rest. Exposed part of each valve has crowded, minute, circular, evenly distributed granules, except on dorsal keel which has longitudinally arranged ridges and grooves . Valve colouration is variable though generally pale with mottled or streaked combinations of white, yellow, brown, black or green; the keel often contrasting with rest of valve. Underside of valves bluish or white bluish. When removed from girdle, intermediate valves relatively elevated with a definite keel.
The wide fleshy girdle possesses 18 conspicuous tufts of thin, numerous bristles up to about 2mm in length. These are transparent, sometimes colourless, often tinted shades of yellow, brown, pink, magenta or green for part or all their length . The rest of the girdle is densely covered by short, slender spines (0.01-0.015mm in length) with longer more robust spines (up to about 0.5mm) scattered amongst them. The edge of the girdle is fringed by a row of spines up to a length of 1.25mm, though generally less than this. The colour of girdle is variable including white,yellow, ochre, pink and magenta.
- Acanthochitona crinita has a narrower girdle and more variable oval or tear drop shaped granulation on the valve surface.
Lives on the underside of rocks and boulders usually lightly embedded in sand or gravel. When displaced from substrate, can roll into a ball . It feeds by grazing material from the rock surface using its radula. Most common in the low shore or shallow subtidal areas but can occur to a depth of 70m.
A southern species occurring from the south of the British Isles to the Mediterranean Sea, the Black Sea, the Azores and the Canary Islands. It is a relatively uncommon species in Britain whose distribution is still poorly understood.