Panamic Bonnet Shell, Semicassis centiquadrata

Panamic Bonnet Shell, Semicassis centiquadrata. Shell courtesy of the commercial fishermen of the greater Los Cabos area, Baja California Sur, January 2014. Size: 4.0 cm (1.6 inches) x 3.0 cm (1.2 inches).

The Panamic Bonnet, Semicassis centiquadrata (Valenciennes, 1832), is a gastropod mollusk member of the Cassidae Family of Helmets. They are also known as the Centiquadrata Helmet and in Mexico as casco granuloso del Pacifico. The shell has a globe-like shape with a low spire that is sharply pointed and a knobbed shoulder. They are marked with evenly-spaced ribs spiraling down the body whorl. The aperture is wide in the center and narrows at both ends; the outer lip is thick and the inner lip of the aperture is wide, with a granular texture. The shell is ivory colored, usually with spiral bands of brown or light orange. In some individuals, these bands are interrupted by ivory axial lines, yielding a pattern of squares. Panamic Bonnet Shells reach a maximum of 8.3 cm (3.3 inches) in length and 6.2 cm (2.5 inches) in height.

Panamic Bonnets are found on and within sand substrate in the intertidal zone to depths of 10 m (35 feet). They are found throughout the Sea of Cortez, and south to Peru; they have not been documented from coastal waters along the west coast of Baja.

Synonyms include Cassis centiquadrata, Cassis corrugata, Cassis doliata, and Cassis lactea.