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Abstract

Without a doubt nematodes are the most species-rich taxon on earth. They are ubiquitous and numerous and a nematode free place is hard to find. Yet they are difficult to identify due to their tininess and their scarcity in morphologically informative characters. We work on the nematode family Diplogastridae. One member of this family is the species Pristionchus pacificus, a nematode established as satellite system for comparison with the model nematode Caenorhabditis elegans. After finding the ecological niche of the nematode (necromenic on scarab beetles) we did a large-scale search for new strains and species in the genus Pristionchus. Newly isolated nematodes have to be brought in culture and identified. For identifi- cation we use molecular markers, which give information on species identity and also help in calculating molecular phylogenies. Species identity is then confirmed with mating experiments. We formally describe new species combining morphological and molecular information and try to set a new standard for nema- tode species descriptions. World-wide sampling gave us a multitude of nematode taxa (not only from the genus Pristionchus but also from many other genera) which we all keep in live and frozen cultures and which help us understanding diversity patterns and phylogenetic relationships. We study biogeography and invasion/introduction in Pristionchus and also look at an example of coevolution of a diplogastrid genus with bark beetles. Taken together, nematodes might not be easy to work with initially but the amount of information and data we can get from that system is highly rewarding.