Similar to the eastern Australian species A. tentoriiformis (Jonas) but differs in the characters of the operculum and the umbilical region. The shell is conical, with a sharp periphery, the whole dorsal surface covered by a chalky coating. Base flat, with dense spiral lirae. Adjoining the concave columella is a narrow, violet basal callus which has, on its lower part a short groove. Operculum brilliant violet, centre fairly depressed, lighter in colour in lower part, being more rose-red, whereas the upper part is indigo-coloured. Dimensions: height 30 mm; diameter 40 mm.

High-spired; whorls flat-sided, with finely scaled spiral threads and a sharply angulate and slightly expanded peripheral rim; base with numerous scaly spiral cords and a rather wide callus over the umbilical area; operculum oval, smooth. Fawn, umbilical area, parietal wall and columella blue. 5 cm.

Low tide, On rocks, Shark Bay, Western Australia, Australia, 35.8mm.
Astralium tentorium is one of a few outstanding turbinids that produce vivid blue opercula. The colouration of its operculum is actually quite variable, ranging from blue to a dark purple and even blue ones often carry a tinge of purple near the nucleus. An algae-grazing gastropod inhabiting low tide zone of intertidal areas and shallow subtidal waters to about -5m, it is often found on or under rocks. Endemic to Western Australia and although a locally common shell, it is uncommon in the international shell trade market. The dorsum is generally rough and eroded, but the base is brilliant yellow in colouration with delicate squamose sculpture. Typical shell length around 40mm., very large specimens may exceed 50mm.

This species is restricted to Western Australia, ranging from Cockburn Sound to Bernier Island off Shark Bay (Ponder 1975). The genus Astralium is considered to be the most appropriate location for this species. The reasons for the use of this name as a full genus will be discussed in detail elsewhere.
Locality
Station 25, Surf Point, Outer Bar, at entrance to South Passage, Sharks (= Shark) Bay, north-western Australia, 0.5-3.5 m, sand and rocks with coral (holotype) (reg. no. 67358).

Australia. Hopetown to Shark Bay, WA. Common in the sublittoral zone.