Emigration Creek Project
Ecology 340
Westminster College, Salt Lake City, Utah
Tessa D. Roden
BONNEVILLE SPRINGSNAIL
Pyrgulopsis transversa
Where are these snails found?
What do they look like?
What do they eat / what eats them?
How do they move?
How do they reproduce?
Snail Anatomy
How do they breathe underwater?
Why does the snail population of the creek change seasonally?
How does water purity affect snail population?
References
(picture)
Where are these snails found?
The Bonneville Springsnail can be found in Emigration Creek on the Westminster College campus as well as other locations in northern central Utah counties. It typically clings to the underside of rocks in Emigration Creek along the stream bottom.
What do they look like?
These snails are small, with a shell of 3 to 5 millimeters in length. The shell is dull brown in color. The shell appears smooth, but with close examination fine growth lines may be seen. The coils of the shell are called whorls, and the springsnail specimens we took from Emigration creek had shells of 3 to 4 whorls.
What do they eat / what eats them?
These snails are vegetarians, feeding on diatoms found on rocks along the stream bed. The snails in turn provide food for leeches and Cutthroat trout in Emigration Creek. Occasional mallard ducks and frogs in the creek may also eat snails.
How do they move?
Snails move using several important muscles. The columellar muscle is attached to the shell internally and is used to withdraw the snail's body into its shell. The foot, which is mostly muscle tissue, is the main source of propulsion for the snail. The front end of the foot secretes a tin, flat ribbon of mucus for the snail to move along. When the snail is caught in vegetation or out of the water it may move by "hunching", or muscular contractions of the foot along with a jerky pulling forward of the shell.
How do they reproduce?
These snails have separate sexes, unlike some other species of aquatic snails which are hermaphroditic. The male copulatory organ, called a verge, is located at the base of the right tentacle. The female reproductive pore is located at the edge of the mantle (shell) cavity. Eggs are laid in a gelatinous mass, usually during spring although egg-laying may continue as late as summer or early fall. The young snail develops within the egg mass, and by the time it leaves it looks like a miniature adult.
Snail Anatomy
Digestive System:
Snails have sets of jaws inside their mouths used to cut off bits of food. Just behind the jaws the digestive tract is swollen to form a large buccal mass with muscles attached. This area is covered by the radula, the snail version of the human tongue. The radula moves back and forth very rapidly to grind up pieces of food. It wears away with use, but is continuously replaced since it is formed in a radular sac at the end of the buccal mass and grows constantly, like the human fingernail. The teeth are fastened to the radula in rows. Snails may have up to thousands of individual teeth, with tiny cutting points called cusps. The esophagus leaves the buccal mass and passes from the foot into the visceral mass within the shell to form a crop. A pair of salivary glands line the crop or esophagus. Behind the crop is a dilated stomach, which is followed by the long intestine, whose posterior end is dilated to form the rectum. The anus opens into the mantle cavity near the edge of the mantle and the shell. A large digestive gland called the liver empties into the stomach as well.
Circulatory System:
The heart of the snail is found on the left side and consists of one auricle and one ventricle. The ventricle pumps blood through an aortic trunk to all parts of the body through a series of arteries and capillaries. From the capillaries the blood passes into sinuses, or spaces in the tissues called the hemocoel. From the hemocoel blood passes into the veins and back to the auricle. The blood contains a dissolved compound called hemocyanin which transports oxygen, like hemoglobin in human blood does.
Nervous System:
The greater portion of the gastropod nervous system, called the brain, consists of nine large ganglia, eight of which are paired. They are connected to each other by commissures and are found around the esophagus just behind the buccal mass. Large branching nerves originating in these ganglia innervate all parts of the body, while several small ganglia are associated with sense organs.
Senses:
Snails have well-developed eyes at the base of their tentacles. Their sense of hearing is centered in two tiny sacs called statocysts, which contain fluid in which bodies called statoliths are suspended. The snail uses its "hearing" more as an ability to detect vibrations and maintain a sense of equilibrium. Taste is centered in the mouth region, where Semper's organ is the organ of taste.
How do they breathe underwater?
Respiration in snails is aquatic and occurs through an internal gill, or ctenidium. The ctenidium consists of a series of narrow, flat leaflets well supplied with blood and arranged like the teeth of a comb. The ctenidium is located on the surface of the mantle cavity of the body whorl (first whorl of shell). A small amount of oxygen may also be obtained through the general body surface.
Why does the snail population of the creek change seasonally?
Snail population in the creek varies seasonally due to a variety of causes including availability of food sources and physical characteristics of habitat. The diatoms which the snails in Emigration Creek feed on are more plentiful in the fall due to increased amounts of minerals (Nitrogen and Phosphorus) in the stream from leaf fall. This may cause growth in snail population. The creek decreases in temperature and increases in speed and amount of water in the winter, which leads to less snails in the creek because they prefer relatively shallow, calm waters.
How does water purity affect snail population?
Snails need high amounts of dissolved salts, especially calcium carbonate, in the water they live in. These materials are essential for shell construction. Generally, soft waters contain few individuals and species, while hard waters contain a great variety of individuals and species. High concentrations of dissolved oxygen in water are also necessary for these snails. Pollution limiting the amount of oxygen available causes snails to disappear from an ecosystem.
References
1. Chamberlain, Ralph V. and David T. Jones. 1929. A Descriptive Catalog of the Mollusca of Utah. University of Utah, Salt Lake City, UT.
2. Oliver, George V. and William R. Bosworth III. 1999. Rare, imperiled, and recently extinct or extirpated mollusks of Utah[:] a literature review. Publication number 99-29. Utah Division of Wildlife Resources, Salt Lake City. (http://www.rsgis.usu.edu)
3. Pennak, Robert W. 1953. Fresh-Water Invertebrates of the United States. The Ronald Press Company, New York, NY.