The food of Planaria torva (Müller) (Turbellaria-Tricladida), a laboratory and field study

The food of Planaria torva was examined in the laboratory by exposing a range of potential prey to the triclad and observing prey mortality. Under these conditions P. torva fed mainly upon tubificid oligochaetes and gastropods. The former activity was regarded as untypical of the field situation and due to limitations of the laboratory habitat. The food of P. torva was determined in the field by taking monthly samples from October 1967 to May 1969 of a population living in Linlithgow Loch, West Lothian, Scotland. A serological technique was used to examine the gut contents of the field triclads. For reasons explained in the text, the prey organisms tested for serologically were gastropods, oligochaetes (Tubificidae), Asellus and chironomid larvae. Planaria torva fed most extensively on Gastropoda, Asellus was the second main food while Tubificidae and Chironomidae were taken only seasonally and in small numbers. The limited extent of feeding on tubificids supports the laboratory data. Small P. torva gave proportionately fewer positive reactions to the prey antisera than large individuals. This was explained by the fact that small individuals occurred most frequently in the warmer months and took smaller meals; both of these features shorten the detection period of food in the gut and therefore give fewer reactions. The diet of small and large P. torva was similar in the field and showed considerable overlap with that of Dugesia polychroa. The food of Polycelis tenuis, Dendrocoelum lacteum and Dugesia polychroa in Linlithgow Loch was described on an annual basis and the results confirmed earlier observations.