Adults may reach a length of 20 mm. The colour is predominantly brown, paler in the juveniles, with numerous dark brown areas each of which contains a brilliant blue spot. The dorsum bears abundant spiculose, clubbed tubercles, each of which has a dark red or black apical spot. There are three tripinnate gills anterior to the anal papilla, protected by three tuberculate pallial lobes. Approximately five tubercles ring the rim of each rhinophore sheath. The rhinophores are smooth and cylindrical; short, rounded oral tentacles are present on each side of the head.
A. punctilucens is extremely well camouflaged in its natural habitat, among sponges (Leucosolenia spp.) upon which it feeds. In shallow waters, with only rare deep records, to 100 m.
It has been recorded from unpolluted shallow waters in the northern North Sea; elsewhere from Norway to the Mediterranean Sea (Distr. A. punctilucens).