Angle-mouth Nutmeg Shell, Trigoniostoma gonostoma

Angle-mouth Nutmeg Shell, Trigoniostoma gonostoma. Shell collected off the beach at Punta Chivato, Baja California Sur, April 2022. Size: 3.1 cm (1.2 inches) x 2.4 cm (0.9 inches). Collection, photograph and Identification courtesy of Colin Campbell, DVM, Punta Chivato, Baja California Sur.

Angle-mouth Nutmeg Shell, Trigonostoma goniostoma. Shell collected off the beach in the greater Los Cabos area, Baja California Sur, May 2008. Size: 3.2 cm (1.6 inches) x 2.6 cm 1.0 inch), November 2018. Collection, identification and photo courtesy of Bob Hillis, Ivins, Utah.

The Angle-mouth Nutmeg, Trigonostoma goniostoma (G. B. Sowerby I, 1832), is a gastropod mollusk that is a member of the Cancellariidae Family of Nutmegs. They are also known as the Rigid Nutmeg. The shell is angular in overall appearance, with four or five straight-sided, very wide whorls, giving the spire a teared look, like a wedding cake. The shell has strong spiral and lengthwise ribs that form knobs, where they cross each other, on the sides and broad, deep shoulders of the whorls. The body whorl is large and the aperture is triangular. When viewed from the bottom, a deep pit (umbilicus) that runs through the center of the shell, to the spire is evident. They have 7 or 8 varices per whorl. Their columellar plicae (teeth) are present but not prominent. The exterior of the shell is cream to light tan in color, with darker brown lines and blotches on the shoulder areas; the interior is white. Angle-mouth Nutmeg Shells reach a maximum of 3.5 cm (1.4 inches) in length and 2.4 cm (0.9 inches) in height.

The Angle-mouth Nutmegs are found within sand substrate in the intertidal zone to depths up to 15 m (50 feet). They range from Magdalena Bay, Baja California Sur to Panama, including the Galapagos Islands. They are found throughout the Sea of Cortez.

A synonym is Cancellaria goniostoma.