(Pennant, 1777)
Description (shell):
Elongate oval, about two and a half times long as broad. Shell valves strongly arched, with a moderate rounded keel and pronounced beaks. Sculpture of longitudinal ridges on the keel, laterally with large, flat-topped, pyriform granules, varying in size and unevenly spaced. Girdle with 18 dense tufts of bristles (up to 1 mm long), one situated on each side, close to the junction between each pair of plates and four in an arc anterior to the head valve; surface with fine, irregular granules interspersed with recumbent spines, fringed with dense series of long (up to 0.5 mm) acicular spines (A. crinita-drawing).
Size:
Up to 34 mm long.
Colour:
Very variable: off-white, grey, yellowish, chestnut, green, olive, brown and shades of blue; in patches and streaks, or marbled; rarely unicolorous.
Habitat:
Lower shore and sublittoral.
Distribution:
Common in the North Sea (Distr. A. crinita).