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A BLOOD-SUCKING SNAIL: THE COOPER'S NUTMEG, CANCELLARIA COOPERI GABB, PARASITIZES THE CALIFORNIA ELECTRIC RAY, TORPEDO CALIFORNICA AYRES

Feeding habits of the over 200 living species of Cancellaridae are largely unknown. The Cooper's nutmeg, Cancellaria cooperi, was seen by divers on the dorsal surface of Pacific electric rays, Torpedo californica. C. cooperi was observed to parasitize electric rays in the laboratory. The snails made small cuts on the ray's ventral surface and inserted their proboscises into the wounds. Snails were also observed to insert their proboscises into the mouth, gill slits, and anus, as well as previously existing wounds. After insertion of the proboscis, the snails appeared to suck blood from the ray. In Y-maze experiments, the snails actively sought out electric rays, but not other common California bottom fishes. Host location appeared to be by chemosensory means. In the absence of electric rays, snails remained buried in the sand without moving for at least 12 days. Field observations indicate that snails may travel as much as 24 meters in search of rays.