One-horn Rock Shell, Ceratosoma monoceros

One-horn Rock Shell, Ceratosoma monoceros. Shell provided by the commercial fishermen of the greater Los Cabos area, May 2016. Size: 2.8 cm (1.1 inches) x 1.5 cm (0.6 inches).

The One-horn Rock, Ceratostoma monoceros (G.B. Sowerby II, 1841), is a gastropod mollusk that is a member of the Muricidae Family of Rocks, that derive their name from the single, tooth-like, projection on the outer lip of the aperture. The shells consist of six whorls, they are sculpted with three varices with nodes in between and numerous spiral ridges, a covered siphon canal and a moderately size aperture that has fine nodes inside the outer lip. Both the inner and outer lips are flared. The exterior of the shell is gray to reddish brown in color; the interior is white. The One-horn Rock Shells reach a maximum of 6.0 cm (2.4 inches) in length and 3.2 cm (1.3 inches) in height.

One-horn Rock Shells are found attached to rocks. Their depth range has not been determined. The shells are found on the west coast of Baja from San Ignacio Lagoon, Baja California to Cabo San Lucas, Baja California Sur. They are not known to the Sea of Cortez.

Synonyms are Murex aciculiger and Murex monoceros.