A group of unsegmented worms which have been variously recognized as an order, class, and phylum.
One of the most common phyla of animals, with over 80,000 different described species (of which over 15,000 are parasitic). They are ubiquitous in freshwater, marine, and terrestrial environments, where they often outnumber other animals in both individual and species counts, and are found in locations as diverse as Antarctica and oceanic trenches.
unsegmented worms with elongated rounded body pointed at both ends; mostly free-living but some are parasitic
