A survey of some of the algal epiphytes on the shells of freshwater mollusca

Abstract

The epiphytic chlorophycean algae have been studied from different species of freshwater mollusc, including a variety of gastropods living within a few feet of the water surface and a number of lamellibranchs found usually either in or on the water bed. The animals were killed with chloroform, the bodies removed and the shells, after washing, were cultured in Soil Solution in glass dishes. The algae were present in a very reduced state - due probably to their being browsed by other snails, but after several weeks in the laboratory they grew to maturity and could be subcultured and identified. Over one hundred forms of algae were isolated the majority of which were thought to be separate species; most of them belonged to the Ulotrichales, the Chaetophorales and the Oedogoniales. The population in general seemed to bear very little relationship to the species of mollusc. The size of the snail, its speed of movement, the shell surface and shape did not appear to affect the species of algal epiphytes. Apart from one species the epiphytes on the bivalves were very similar to those on the snails although there were differences in the frequency with which each occurred. Empty snail shells had populations almost identical with those on living specimens if the shells remained in the same environment. As far as could he discovered no relationship existed between the composition of the shell and the algal epiphytes. The cells of a species of Oedogonium were larger on snails in a pond than on adjacent stationary objects. A number of algae have been shown to pass almost unharmed through a snail's gut. Inter-relationships of snails and algae are discussed.