Body with a fairly large disc and 5 rather short, stiff and tapering arms; up to 100 mm in diameter (occasionally 200 mm); R/r: 3,5-4,5. Coloured reddish-violet or yellowish, with or without purple marks.
The upper surface is covered with paxillae. The upper and lower rows of marginal plates are well-marked. The upper marginal plates generally with a larger, conical spine, especially in the outer part of the arms. The lower marginals are flattened, rectangular, and at their upper end bear 4-5 large marginal spines in an oblique series that passes downwards along the outer edge of the plate. There is only one series of ventro-lateral plates in the oral interradial area (A. irregularis test).
The adambulacral plates each bear 3 equal-sized furrow spines; no pedicellariae. The tube-feet are pointed and suckerless, and are provided with double ampullae (A. irregularis tube foot).
This species prefers sandy bottoms, in which it buries itself so as to lie concealed. It is occurs at depths from 10-1000 m.
This species is distibuted from Norway down to Morocco, probably even to the Cape Verde Islands.