SCHMIDT-RHAESA, A.: The two dimensions of biodiversity research exemplified by Nematomorpha and Gastrotricha

Biodiversity research is characterized by two dimensions: the horizontal dimension recognizes species, their spatial interrelationships and patterns such as biogeographical distribution. The vertical dimension tries to explain the history of the recent biodiversity through phylogenetic and evolutionary approaches. The horizontal dimension is illustrated by Nematomorpha (horsehair worms). The standard of species descriptions has to be raised and reinvestigations are necessary, if statements according species numbers, distribution patterns, impact on their host population and the role in the ecosystem should be substantial. The vertical dimension is illustrated by gastrotrichs. Recent hypotheses about their placement differ, either including them in the Spiralia (molecular data) or placing them basal to Cycloneuralia/Ecdysozoa (morphological data). In both hypotheses, however, gastrotrichs are a very basal bilaterian taxon and therefore have a potentially solid impact on the phylogeny of this taxon as well as the reconstruction of it�s ancestor.