The Aschelminthes Phylum Nematoda

General Information The term “Aschelminthes” refers to a large group of about ten different phyla of soft- bodied worms Of these, the phylum Nematoda is the most important Examples include Ascaris and Trichinella Aschelminthes also include the phylum Rotifera

Nematoda: Habitat Are free-living, found on land and in marine and freshwater habitats Are also important parasites on plants, animals and humans

Nematoda: Characteristics Bilateral symmetry 3 cell layers Organ level of organization Cephalized Have a complete digestive system with a mouth and anus Have a “tube within a tube arrangement” called a pseudocoelom

The Pseudocoelom Body cavity between intestine and body wall Contains fluid which creates hydrostatic pressure When muscles in the body wall contract the pseudocoelom gets smaller and no pressure is applied to the intestine

The Pseudocoelom Contains reproductive organs (ie. The sperm and egg) Stores wastes Fluid inside distributes nutrients and O 2 (no circulatory/respiratory systems)

Nematoda: Digestive System Mouth and anus make up a “complete digestive system” Food enters the mouth through the pharynx and then into the intestine where nutrients are broken down and absorbed; wastes leave out the anus No stomach… just a tube

Nematoda: Excretory System 2 tubules that run the length of the body join at the anterior end and empty out an excretory pore – mostly excretes salt, nitrogenous wastes exit through diffusion of the body wall

Movement and Nervous System 4 nerve chords: dorsal, ventral and two lateral chords A dense nerve ring surrounds the pharynx at the anterior end – “brain” They only have longitudinal muscles Their movement is serpentine s_elegans#/media/File:CrawlingCelegans.gi fhttps://en.wikipedia.org/wiki/Caenorhabditi s_elegans#/media/File:CrawlingCelegans.gi f

Reproduction Reproduction in Nematodes is sexual Most nematodes are dioecious – meaning there are separate male and female individuals. Some are hermaphrodites

C. elegans is a free living nematode about 1mm in length. They contain 959 cells as a “female” and 1031 cells as a male… always. This makes them very desirable for research.

Ecological Importance of Nematodes Important in aerating soil and distributing organic materials and minerals in soil Infest crops, livestock and humans causing disease –Eg. Hookworm, trichinosis, crop damage This allows them to live in a less competitive environment

Trichinella

Ascaris Slender, cylindrical, pointed at both ends, a parasitic roundworm Can measure up to 1 foot Lives in humans, pigs, chickens, cats, dogs, horses, and other mammals Reproduce sexually with separate sexes

Eggs are in feces Eggs in food or H 2 0 enter host Hatch in Intestine Larvae enter blood vessels into the lungs In the throat, they are coughed out of the lungs and swallowed into the stomach Larvae mature and male and female fertilize Life Cycle of Ascaris

Other Nematode Diseases Elephantiasis is a disease caused by the nematode Wuchereria bancrofti Adults of the parasite live in the lymph nodes of humans Repeated infections can cause the lymph nodes to become blocked, and fluids to accumulate Elephantiasis is transmitted by a mosquito vector

Warning the pictures of the pathology of this disease are quite graphic – If you are easily disgusted don’t look!

Anisakis is a nematode parasite of fish and than ultimately marine mammals. Occasionally, by eating raw fish, humans can be infected by this parasite.