Aschelminth phyla

The aschelminths are a large and heterogeneous group also known as the Nemathelminthes, or Pseudocoelomata. These terms are now rarely used and they are now classified as ten or so separate phyla. The main characteristics that hold these phyla together in what is now recognized as a loose grouping is a psudocoelomate body plan, specializations of the pharynx and specialized cuticular structures. The aschelminth phyla may form one one monophyletic group.

Phyla generally considered to belong to the aschhelminth phyla include...

• Phylum Nematoda; the roundworms. The parasitic forms get most of the press, but the majority of them are important for ecological processes and are free-living. Some claim that they are the most numerous animal populations on earth. (PIX)
• Phylum Nematomorpha; the horsehair worms. These guys are obligate parasites of arthropods. They have an extraordinary life cycle that starts with soil-dwelling larvae that are found in moist, low-lying areas. When an arthropod ventures into an infested area the larvae burrow into the arthropod and set up shop in the coelom. There, they metamorphose into the adult worms. Some can be as much as a meter long and are spiraled into a knot (which is why they are sometimes referred to as  Gordian worms). Then, within their host they begin eating various organs while still keeping the host alive. Finally, they eat portions of the brain resulting in a behavioral change that causes the host to seek water. The adults then burrow out of the hose, mate, and then lay eggs in the water to complete their life cycle. They received their common name because they were often found in horse troughs and were once thought to be an example of spontaneous generation. (A horse would drop a hair from its mane and that hair would acquire life; PIX)
• Phylum Rotifera; the wheel organ animals (named for their peculiar feeding/locomotion organs found at the interior end of the beast). all are free-living. (PIX)
• Phylum Chaetognatha; the arrow worms. The arrow worms are free-living marine predators. (PIX)
• Phylum Priapulida; Free living marine organisms also known as "penis worms". There are only a few dozen species today but they were quite common during the Cambrian. (PIX)
• Phylum Gastrotricha; These are free-living marine forms. They are also known as "water bears" because of their peculiar locomotion (PIX)
• Phylum Loricifera; There is no common name for these creatures since they are the most recently identified phylum. They are marine, free-living, and have a jointed external skeleton known as the lorica. (PIX compare body to a lorica)
• Phylum Cycliophora; the wheel wearers. This is a parasitic life form feeding on lobsters as adults. There is only one known species. (PIX)