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Wednesday, Nov. 9, 2005

ANIMAL TRACKER

Mystery snail Tanishi


* Japanese name: Tanishi
* Scientific name: Cipangopaludina japonica
* Description: A large snail, growing up to 60 mm long. It has two large "horns"; shell color is uniform, light to dark olive-green, but may have color bands. As in the photo, they are often muddy, and they are also known as mud snails.
* Where to find them: In quiet lakes and ponds and in slow-moving streams all over Japan. They are also found where they aren't wanted: in Canada's Great Lakes and all over the United States. How did they get there? They was introduced by immigrants who brought them over as a food source.
* Food: The snails have a strong, rasping tongue (the radula), which they use to scrape algae from the surface of large rooted plants. They do not, however, eat the larger plants themselves and avoid areas where they live, such as rice paddies. Mystery snails also consume large amounts of bacteria, lots of rotting vegetation and even sewage sludge from wastewater treatment works. This has led some people to suggest that mystery snails be deployed at sewage outlets, to help clean up the sludge. Because the snails eat almost anything, they have out-competed the native snails in Canada and the U.S.; they also out-compete clams and mussels. They are themselves parasitized by organisms that cause human disease, such as intestinal flukes. Another method of feeding they use is the mucus string. The snail drags a line of sticky mucus behind it, which picks up bits of food. From time to time, the snail will turn its head and consume the food-laden mucus.
* Special features: Mystery snails belong to a family called Viviparidae, a name that refers to the fact that they give birth to live young. This is unique among gastropods: all other snails lay eggs that later hatch, but in the mystery snail, the eggs hatch while still inside the female. The juvenile snails stay within the mother's shell until they are large enough to try their luck on their own. As autumn comes to an end and temperatures fall, the snails migrate into deeper waters and go into a kind of semi-hibernation until spring. They have a "trap door" -- a hard disc of muscle on the bottom of the foot, which they use to shut themselves into their shell if danger threatens.

PHOTO COURTESY OF BIO-IMAGE NET



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