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Peritricha; Lymnaeidae; Pond ecology


There are many obscure niches in a, pond that make fascinating ecological studies. The shell of a pond snail such as Physa gyrina Say, is one of these. In this study alone, 18 species of attached animals and plants were found growing on P; gyrina shells. About half of these species occurred on the shells in large numbers and completed a large part of their life cycle there. On P. gyrina, the most abundant animals included three species of protowans and a tendipedid larva. The protozoan species, Epistylus niagarae Stokes, Opercularia ramosa Stokes, and V orticella campanula Ehrenberg all belong to the order Peritrichida (Pl. 1). E. niagarae and 0. ramosa grew in large multi-headed colonies, while V. campanula generally grew in groups of single-stalked heads. These animals were studied in detail in order to determine some of the interrelationships between the animals, the environment, and the host snail. Snails were collected from one Minnesota locality at regular intervals for a period of eighty days and the shells examined under a microscope. At the same time observations were made both on the behavior of the snails and on the environmental conditions. The study showed that both the numbers and species of snail shell peritrichs are largely dependent on the behavior patterns of the snail, which in turn are affected by conditions in the water.

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