The term aschelminth is used for any member of about ten different invertebrate phyla. The Phylum Aschelminthes formerly included all of these phyla as subdivisions, but the term is no longer valid. It is now just a convenient word used to cover these organisms, most of which are microscopic soft-bodied worms. They are also called pseudocoelomates.

Although invertebrate experts do not necessarily agree on these categorizations, organisms that are generally considered aschelminths include the following:

• Phylum Acanthocephala -- parasitic worms armed with spiny probosces; about 1000 species known
• Phylum Chaetognatha -- arrow worms (a marine plankton species); about 100 species known.
• Phylum Cycliophora -- 1 species known: Symbion pandora, a microscopic symbiont of lobsters
• Phylum Gastrotricha -- gastrotrichs, aquatic acoelomates; about 450 species known, all microscopic
• Phylum Kinorhyncha -- kinorhynchs or "mud dragons"; about 150 species known, all microscopic
• Phylum Loricifera -- loriciferans; about 10 species described, all microscopic
• Phylum Nematoda -- nematodes or roundworms; about 20,000 species known, 200,000+ species as yet undescribed
• Phylum Nematomorpha -- horsehair worms; about 320 species known
• Phylum Priapulida -- priapulid worms; about 20 species known, marine, some microscopic
• Phylum Rotifera -- rotifers or "wheel animalcules"; about 2000 species known, all microscopic
• Phylum Tardigrada -- tardigrades or "water bears"; not always considered aschelminths, more similar to the Arthropoda

External links

• Aschelminth information page

Zoology