A rare marine snail living offshore from California and Mexico feeds off one of the ocean’s most powerful electric rays in an unusual parasitic relationship, three biologists at the Scripps Institution of Oceanography here have reported.
The snail, commonly known as Cooper’s nutmeg, inserts its tubular snout into the electric ray and extracts bodily fluids for as long as 40 minutes at a time without any apparent ill effect on the ray. The snail as well suffers no harm, despite the ray’s one-kilowatt electric discharge--equal to the shock from a car battery--that it uses to fend off predators and to capture prey.
The UC San Diego scientists discovered the snail’s feeding habit while they were diving off San Diego, Scripps officials said. Laboratory studies using the snail and electric ray confirmed that the feeding takes place while the ray lies partly buried on the ocean floor.
The work is the first to describe the feeding habits of any of the 73 species to which the Cooper’s nutmeg belongs.
The studies show that the snail finds a ray by sniffing out its chemical trail, even at a distance of 75 feet or more. The Cooper’s nutmeg has a 4-inch-long extendable snout lined with tiny teeth that can pierce the ray’s surface tissue. A tube for transporting the ray’s fluids into the snail also runs along the snout and contains part of the snail’s digestive system.
John B. O’Sullivan, one of the researchers, said, “Early (studies) suggested that the snails fed on soft-bodied microorganisms. However, the length of the (snout) suggested it fed on something it didn’t want to get too close to.”
O’Sullivan said that the chance discovery of the snail feeding on the ray in the ocean proved fortunate, because scientists would not have postulated such a relationship between a docile snail and an electrically armed predator.
Along with colleagues Ron McConnaughey and Michael Huber, O’Sullivan also found that the snail prefers to feed on the bottom of the ray, perhaps because its snout might be mistaken for a tasty worm by other fish if it were visible on top of the ray. The snail may also emit a toxin that functions as local anesthetic on the ray.
In the last three years, the Scripps scientists have collected about 20 snails, of which 80% were caught in the vicinity of a ray. The Cooper’s nutmeg has an uncommonly beautiful shell much prized by shell collectors. The snail is commonly found in ocean waters deeper than 60 feet.