Scotch Bonnet – Semicassis granulata undulata

The Scotch Bonnet – Semicassis granulata undulata: also known as the Mediterranean Bonnet.


The Scotch Bonnet carries the scientific name of Semicassis granulata undulata, which is classed as a Mediterranean sub-species of Semicassis granulata. It falls under the category of sea snail, a marine gastropod mollusk in the subfamily Cassinae, the helmet shells and bonnet shells. The generic name is a combination of the Latin prefix: semi, meaning half, cassis is a noun meaning helmet. The specific taxon name granulata; is derived from the Latin noun grana meaning grain, although used in the diminutive form meaning granulated. Granulated means to be covered in grains, pellets or granules.


The Scotch Bonnet is egg-shaped in appearance and is quite large, 2 to 4 inches in dimension. The shells pattern is regular in colour, with orange, brown or yellowish coloured spots. The surface of the shell is variable: either it can be polished and smooth, have nodulose on the shoulder of the whorls, have a grooved surface or even be granulated. The shell grows an outer lip at different growth stages. The snail rests during growth stages, usually absorbing the entire outer lip before it begins to grow again.

The Scotch Bonnet has a vague resemblance to a tam o’shanter bonnet. Hence the name derived from the appearance of a Scottish, traditional tartan hat.


This species can be found in the Mediterranean Sea and the Atlantic Ocean off Northwest Africa. The Macaronesian Islands also have this sub-species of Semicassis granulata. The Semicassis granulata undulata lives on sandy substrates in shallow waters. It is a predator by nature, searching for food on sandy stretches of ocean floor. Scotch Bonnets are known to eat sea biscuits, sand dollars, sea urchins and echinoderms.

Life Cycle:

The female requires adequate light, abundant food supplies and optimum water temperature for breeding and early growth. In Spring the female deposits hundreds of egg capsules in a tower shaped structure. The tower can be built about 4 to 5 inches in height. The male fertilizes these eggs, which subsequently develop into trochophore larvae. The eggs hatch as free swimming veliger larvae, which will be carried on ocean currents. As the Scotch Bonnet matures, it sinks to the ocean floor and shell growth begins. The shell growth begins at what will later become the 

apex of the shell, and typically rotates clockwise. The Scotch Bonnet reaches maturity in one to six years.


The Scotch Bonnet is preyed upon by vertebrates such as fish, invertebrates too, including crabs and stone crabs. The only defense mechanism the Scotch Bonnet has, is to draw itself into the shell and close the aperture using the operculum.

Photo by Janet Bulmer @ DiveSMART Gozo

Divesite: Mgarr ix-Xini