The Meiofauna Paradox

Project Title: Clarifying cosmopolitan distributions of marine interstitial metazoans and the meiofauna paradox

Funding Source: University

Principle Investigator: Torsten H. Struck, University of Oslo and Günter Purschke

Investigations on evolution, systematics, phylogeny and functional morphology are in the focus of interest. Currently these investigations are carried out on annelids, the segmented worms, and those taxa which are presumed to be closely related to them. Special emphasis is laid to the phylogenetic relationships within and validity of Lophotrochozoa.

Out of the about 35 so-called phyla of Metazoa 23 have at least a few meiofauna representatives and some are exclusively meiofaunal, inhabiting the spaces between the sand grains. The combination of small sizes, absence of pelagic larval (distribution) stages have led biologists to assume restricted distribution of the individual species – at the same time many species were described with distribution ranges encompassing entire continental coastlines, amphi-oceanic or even cosmopolitan distribution. This phenomenon became known as the “meiofauna paradox”. Focusing on a few representatives from the annelids it could be shown that cosmopolitans rarely exist and mostly we are faced with so-called cryptic species. Applying advanced morphological methods and especially molecular markers it could be shown, that there exist meiofaunal organisms belonging to different and clearly separated but almost morphologically identical species. Speciation most likely coincides with an unexpected degree of morphological stasis including species that have diverged about 140 million years ago without recognizable morphological differences.