The life history, growth, and age structure of Nephelopsis obscura Verrill, 1872 (Hirudinoidea) in Alberta

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Abstract
Two generations of Nephelopsis obscura were produced annually in the spring and in the late summer. The spring generation was the progeny of the heavier elements of the previous year's spring generation and of the late-summer generation produced 2 years previously. The late-summer generation was produced by parts of the previous year's spring and late-summer generations. Each generation produced young after either 12 and 15 months or 12 and 19 months although each individual bred once only. Unlike other species of leeches studied N. obscura showed no direct correlation between cocoon production and water temperature, the primary prerequisite being a weight of more than 150 mg. Seasonal movements from the deep-water zone to the shore zone in spring and vice versa in the fall were recorded for the first time. The movements to the deep-water zone were not synchronous throughout the population, the spring generation completing its movements before the other components of the population.

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