Cooper’s Nutmeg Shell, Cancellaria cooperii

Cooper’s Nutmeg Shell, Cancellaria cooperii.Shell collected off the beach of Bahía Concepción, Baja California Sur, October 2019.Size: 9.8 cm (3.9 inches) x 4.3 cm (1.7 inches). Collection, photograph and identification courtesy of Bob Hillis, Ivins, Utah.

Cooper’s Nutmeg, Cancellaria cooperii (Gabb, 1865), is a gastropod mollusk that is a member of the Cancellariidae Family of Nutmegs. The shell consists of six or seven whorls with a high spire and an aperture with an inside edge that is marked with folds. They have a series of knobs along the tops of the whorls, caused by broad ridges that run the length of the shell and very fine spiral lines follow along the whorls. The exterior of the shells are light yellowish brown, with dark brown spiral lines; the interior is white. The Cooper’s Nutmeg Shell is one of the largest members of the family reaching a maximum of 11.2 cm (4.4 inches) in length and 4.9 cm (1.9 inches) in height.

Cooper’s Nutmegs reside in and within sand substrate at depths between 20 m (65 feet) and 200 m (660 feet). While little is known about the feeding habits of most Nutmegs, Cooper’s Nutmeg is an exception. Cooper’s Nutmegs are highly specialized vampire parasites that suck blood from the Pacific Electric Ray, Tetronarce californica. They lie buried in the sand until their chemoreceptors sense a nearby submerged ray. They can crawl distances of up to 23 m (75 feet) and insert their elongated proboscis into an open cut, the anus, gills, or mouth of the ray and begin sucking blood from their victim. They may also use their radula to cut a small incision in the ventral side of the ray as needed. The rays do not appear to be harmed by this behavior. In turn they are preyed upon by the Electric Rays. In captivity, Cooper’s Nutmegs exhibit similar behavior toward Pacific Angel Shark, Squatina californica. Cooper’s Nutmegs range from Central California to Guerrero Negro, Baja California, along the central and northwest coasts of Baja.