A very heavy triangular shell on sand, which hunts urchins by drilling through the test. Usually found buried with only a ridge showing.
Shell to about 41 cm, which makes it the largest sea snail in the western Atlantic. Very large, heavy and triangular in outline, with a short spire and three spiral rows of blunt rounded knobs, with smaller folds between. White to tan with brown blotches. The identification is the big glossy shield beside the aperture: in this species it is rounded or oval, cream to salmon, with brown or black markings between the teeth of the opening.
The other two Caribbean helmets are separated on that shield. The king helmet has a triangular shield, solid black between the teeth, and seven or eight dark stripes on the outer lip, and reaches about 30 cm. The flame helmet has a rounded shield with no dark markings between the teeth, and reaches about 13 cm.
It is a sea urchin specialist. It lives on open sand flats and seagrass margins down to about 100 m, buried by day and hunting at night, and divers usually find a plough mark in the sand leading to a buried animal.
Two notes on names. The species name means “of Madagascar” and is a mistake: Lamarck misunderstood where the type came from, and the animal is confined to the western Atlantic. And most shell literature calls it the emperor helmet rather than the queen helmet; both names are in use for the same animal. It is the classic shell for cameo carving, which is why heavy collecting has left it locally depleted.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.