of the snail leech
Distinct physical structures and their functions
Ecological significance to Emigration Creek
COMMON NAME: snail leech (Pennak, R.W.)
DISTINCT PHYSICAL STRUCTURES AND THEIR FUNCTIONS
(Glossiphoniidae taken from Ginsberg, D. Natural history of leeches.)
|sucker||substrate attachment; locomotion|
|clitelum||secretes membranous capsule around |
eggs (not a true cocoon)
The snail leech has a 3 part life cycle: egg, membranous capsule, and adult. All leeches are hermaphroditic and reproduce sexually. Cross fertilization occurs when one leech fills a spermatophore and attaches it to another leech. The recipient absorbs the sperm from the spermatophore. The sperm travel to the ovaries via the coelom (Ginsberg, D.). Snail leeches immediately cover their eggs with a membranous capsule. The capsules are fastened to the parent leech. Young snail leeches remain attached to the ventral surface of their parent until another live substrate is found (Pennak, R.W.).
Glossiphonia complanata only occupies freshwater watersheds such as Emigration Creek. Being a poor swimmer, it prefers static to moderately moving water so that it won’t be washed away in the rapids. Many snail leeches are found near the Emigration Creek storm drain located at the east end of the Westminster College campus. The water must contain items that it can conceal itself under such as plants, stones and tree leaves. Leech populations are typically 700/m2. Studies show differential species domination according to specific chemical characteristics of the water, particularly calcium concentrations. Water temperature is irrelevant to the leech (extremes excluded). Alkalinity is a requirement for leech survival with pH levels above 5.0 desired. The presence of dissolved oxygen is also required. Turbidity and salinity are thought to play small roles. Leeches have a high tolerance for pollution including eutrophication, oil, copper sulfate and pesticides. They have no tolerance, however, for zinc (Ginsberg, D., 1998).
When it comes to predation, leeches tend to be species specific. As its common name implies, the snail leech of Emigration Creek feeds primarily on snails and occasionally on trout. The snail leech will drain the snail of its body fluids and then suck soft tissues through its proboscis. The manner in which some Rynchobdellida (including the snail leech) are able to take blood from vertebrates is not understood since they lack teeth to make an incision. It is speculated that digestive enzymes are secreted by the proboscis which are able to digest delicate tissue layers like those found near trout gills (Pennak, R.W., 1989).
ECOLOGICAL SIGNIFICANCE TO EMIGRATION CREEK
The snail leech is a carnivore, feeding on the snails and possibly the trout that inhabit Emigration Creek. The snail leeches are preyed upon by the trout and possibly the creek’s various carnivorus aquatic insects including stauflies, but neither of these predatory macroinvertebrates which are indicative of high quality streams are currently found in Emigration Creek. The seasonal abundance of snails and segmented worms functioning as major detrivores on tree leaves may explain the abundance of snail leeches in Emigration Creek.
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1. Ginsberg, D. 1998. Natural history of leeches.1998.
2. Pennak, R. W. 1989. Freshwater Invertebrates of the United States. John Wiley & Sons, New York, N.Y.