Today, these organisms are classified in about ten separate phyla. Opinion is divided as to whether or not the aschelminth phyla form one monophyletic group.
Nematodes make up the second most diverse animal phylum, second only to the arthropods .
Free-living nematodes are exteremely abundant in soils and sediments, where they feed on bacteria and detritus. Other nematodes are plant parasites and may cause disease in economically important crops. This cavity has traditionally not been considered a true coelom, because it supposedly does not exist within the mesoderm, true mesenteries are not present, and its development in the embryo is quite different. Body cavities develop in several different ways and perform many different functions within the animal kingdom. This is known as cryptobiosis .