Observations on the Biology of the Snail Lymnaea stagnalis appressa During Twenty Generations in Laboratory Culture

Abstract

During course of last one hundred years various notes and papers have appeared presenting observations on life history and culture of numerous lymnaeids; in last two decades emphasis of research on this subject has been placed increasingly on an experimental investigation of factors governing growth. A review of results of these investigations indicates that Lymnaea is well adapted to serve as a dependable, easily handled, normal, healthy, experimental mollusc of conveniently small size, of short life cycle, and available in quantity and in various stages of development throughout year. This genus is endowed with further desirable qualities: many of its species occur over a wide geographic range, are fairly constant in form, have been1 popular laboratory material for over eighty years (certain species such as L. stagnalis have been studied more intensively ecologically, physiologically, histologically, morphologically than any other basommatophoran pulmonate), and are probably tlhe highest form of animal life in evolutionary series in which self-fertilization occurs (Baily, 1931). In parasitological field, these snails are also important as vectors of parasites of man, domestic animals, wild game and fish. In this connection, KrulI (1931) in a paper on importance of laboratory-raised snails in helminthology, writes: Life history studies are rapidly occupying attention of helminthologists throughout world, and this phase will soon be on a par with taxonomic investigations in group. The snail is almost indispensable in life history work on trematodes. In an effort to develop further potentialities of Lymnaea as an experimental gastropod, this paper attempts, through integrated contributions of numerous earlier researchers and by additional original investigation on L. stagnalis appressa Say to present a simple, inexpensive, reliable method for culturing it in quantity. Observations on life history of L. s. appressa cultured in this laboratory for twenty generations over a period of six years are also reported. This snail, besides its excellent response to laboratory culture, has added characteristic advantage of possessing a relatively thin semitransparent shell which permits inspection of many of internal organs in living, undisturbed animal. Certain environmental conditions have been described in literature as improving growth and fertility in lymnaeids. Boycott (1936) in studying native habitats of freshwater Mollusca in Britain, came to conclusion that the more important features of favorable habitats are (1) cleanliness of