Annelida

The group of annelids is evolutionarily successful, with between 10,000 and 20,000 described species (slightly more than 11,500 polychaetes listed on the platform "WORMS - World Register of Marine Animals") colonising almost all habitats (with the exception of the Arctic and the air), but the majority live in or on marine sediments and hard substrates. The large differences in the number of species already indicate one of the "main problems" of the animal group: Although scientists, amateur biologists and explorers have been working on worm-like animals for more than 200 years, it often takes the combination of morphological and molecular methods for an exact classification. [more]