A. Faunistics, biogeography and ecology of free-living platyhelminthes
Free living platyhelminthes (terrestrial microturbellaria) live within water films associated with soil particles or fill pore spaces. Our knowledge on these species is limited, as these are poor in characteristic signs and difficult to investigate. The situation is further complicated by the fact that there is no complete and generally valid identification key, but rather only attempts to develop keys for individual groups and genera. About 30 species are known from soils of Central Europe; the number of unidentified species may be manifold higher.
Ongoing faunistic investigations are recording plathelminth communities in semi-natural deciduous forest sites in Central Europe, with a focus on Eastern Germany. The diversity of the species, their correlation with different types of soil strata and specific habitats and the seasonal variations of the communities are investigated over the year.
A mixed beech forest near Görlitz has been regularly sampled as a permanent study area since 2010. At the beginning monthly sampling was carried out and from 2012 on every season. With the help of the abiotic data acquired in addition, their influence on the abundances of the individuals during the course of the year and in relation to climatic changes can be observed.
From 2011 onwards, further sites (coniferous forests with and without moss as ground cover, grassland, sandy soils, post-mining landscapes, mofette fields) were recorded and attempts were made to identify differences in species composition.
A further question is the significance of platyhelminthes in soil food webs. Our investigations show that turbellaria feed on nematodes, rotifers, diatoms, tardigrades, thekamoeba and even their own conspecifics. Experiments on the feeding rate with selected species of platyhelminthes and nematodes should provide data on the quantities and the importance of this group as predators.
B. Evolutionary and functional-morphologic investigations
Plathelminthes are poor in submicroscopic characters. Characters relevant for their evolution, however, can be found in their internal organs. We investigate the male and femal sexual organs, protonephridias, different sensory organs and epidermal and neodermal layers. The investigations are carried out in cooperation with colleagues from abroad. Further investigations will focus on the transition from a free living to a parasitic way of live. Not only ultrastructural investigations allow us to recognize steps in evolution, but may additionally contribute to our understanding of the physiology of these organisms. Investigations of the canals of the sexual organs help to understand the transport of semen and eggs. Dermal glands make us understand the rapid attachment to the substrata. Investigations of excretion organs show the transport of metabolic waste and water. Thus, we may be able to correlate morphological adaptation to functional and vice versa.
C. Methods for extraction of free – living Plathelminthes from soil samples
The quantitative extraction of free-living platyhelminths from soil samples has long been a problem. In comparative studies we have tested different methods to find out the most suitable method (in terms of effectiveness and time required). Different extraction methods used for platyhelminths living in marine sediments cannot be applied due to the organic content of the terrestrial soil. In contrast, a seawater ice extraction extracts quantitatively in clear dependence on the salt concentration.
A favourable, time-saving method for the extraction of turbellaria from terrestrial soils is the extraction with gauze bags immersed in fresh water. This method is used as a standard method in our section.