Microturbellaria

The turbellarians are mostly free-living, sometimes commensal or parasitic, non-segmented flatworms with simple life cycles, and equipped with a cellular or syncytial epidermis, which is usually ciliated. The rhabdocoels are small worms, ranging from 0.3 to 3 mm in length. The body shape is either elongated slender or plump, without any characteristic body projections. Still waters are characterised by larger, more sedentary species, whereas the small, faster-moving species are more abundant in running waters.

• There are 492 known species of microturbellarians in running-waters worldwide1. Some streams are inhabited by up to 94 different species of Microturbellaria, but more commonly 5 - 15 species co-ocurr in the same system2. Densities are highly variable seasonally but may reach up to 7.103 m -2.
• Microturbellarians often display a habitat-specific correlation between body size and their activity. Consistently higher densities of microturbellarian species were found in streambed layers below 20 cm sediment depth as well as distinct density differences between pool and riffle sections in an alpine gravel stream3. Thus, the structure of varied microhabitats appear to be the most important factor determing the abundance and distribution of microturbellarians.
• Microturbellarians feed on many different food items, ranging from algae, bacteria, ciliates, nematodes, microcrustacians to oligochaetes and insect larvae. Certain microturbellarian species were found to have a marked impact on the densities of tubificid oligochaetes4.
• Species identification of almost all microturbellarians is based on serial sections, and especially on the detailed anatomy of the reproductive system of a mature individual. The Turbellaria fauna is poorly known and their species identification needs specialist's knowledge1.