A number of specialists at other national and international institutions are engaged in the project too. Worms constitute a great part of the biological diversity, in species richness as well as in structural variation. They are extremely common. In bottom sediments of the sea, worm densities are often of the same order of magnitude, but there the number of different worm groups and species increases considerably. In particular, oligochaetes and nematodes play an important role in the decomposition and mineralization of organic material in soils and sediments.
Many worms feed on microorganisms, others prey on various small invertebrates.
In addition, there are many worms that are parasites on or inside other organsims. The poor knowledge of most worms is partly due to their small size, but also reflects that many worm species are difficult to distinguish from one another. In many cases, worms can only be identified on the basis of the appearance of internal organs. For each of these groups, there are hundreds of species in Sweden, but nobody knows the exact numbers. Realization Compilation of literature data regarding the occurrence of worm species in Sweden.