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).

Phylogeny: The Panamic Bonnet Shell, Semicassis centiquadrata (Valenciennes, 1832), is a gastropod mollusk member of the Cassidae Family of Helmet Shells. The genus Semicassis is one of thirteen genera in this family, and there are thirty-two species in this genus. They are also known as the Centiquadrata Helmet Shell and in Mexico as Casco Granuloso del Pacifico.

Description: The Panamic Bonnet Shell is globose in 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 of the aperture is thick and toothed. The inner lip 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.

Habitat and Distribution: Panamic Bonnet Shells are found on and within sand substrate in the intertidal zone to depths of 10 m (35 feet). They are a subtropical to tropical Eastern Pacific species that are found in all Mexican waters of the Pacific Ocean with the exception that they are absent from the west coast of the Baja Peninsula.

Ecology and Behavior:  Panamic Bonnet Shells are predators that feed primarily on echinoderms. They use their foot and mantle to pin prey to the bottom. They, in turn, are prey for crabs, fish, and other mollusks. They are gonochoric and reproduce sexually, through broadcast spawning. There is no mention in the available literature of them engaging in any types of parasitic, commensal, or symbiotic relationships. From a conservation perspective they have not been formally evaluated however they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.

Synonyms: Cassis centiquadrata, Cassis corrugata, Cassis doliata, Cassis lactea, Phalium centiquadratum, and Semicassis (Semicassis) centiquadrata.