Turbellarian taxonomic database

Abstract / Notes

From 1911-1935 distr. and habitat of 9 spp. of freshwater triclads were studied in Belgium. Attention was
paid to ecological factors as to temp., pH, rate of flow, light and chemical conditions of the water. Only 2
planarians (Polycelis cornuta and P. nigra) are indifferent to pH, the others live only in alkaline water
with an optimum about pH 7. Planaria alpina septentrionalis and Polycelis cornuta are evidently
oligothermal, Euplanaria gonocephala is rather eurythermal. All 3 spp. may be found in winter too. Among the
limnadophil spp. Polycelis nigra is absolutely eurythermal and occurs also in winter, when the other forms
are missing. Planaria alpina was the most reophil sp. As to the amt. of dissolved matter in the water it is
euryhalin, Polycelis cornuta is oligohaline. From the distr. of spp. it may be concluded that competition
with other planarians and altitude of the habitat are not limiting factors. The well known zonation of
rheophil triclads in streams and rivers is not due to one single factor as preceding investigators believed,
on the contrary temp., rate of flow, pH, dissolved matter and quality of the ground regulate the distr. of
the turbellarian fauna as a complex.

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