Aschelminthes are commonly known as roundworms. They are characterized by the presence of a pseudocoelom. It is now an obsolete phylum of invertebrates and the animals grouped under this are now kept in ten different phyla.
Key features of Phylum Aschelminthes
- They are free-living or parasites. They are found in soil, freshwater or as a parasite on plants, animals and even humans. Ascaris is found living as an endoparasite in the human intestine.
- The body is bilaterally symmetrical and triploblastic.
- The body is unsegmented, long, slender and tapers at the end. Metameric segmentation is not found.
- They are dioecious, males are generally smaller than females.
- Animals of this phylum possess pseudocoelom.
- They have an organ-system level of body organization.
- The digestive system comprises a complete alimentary canal with the muscular pharynx. In Ascaris, the rectum opens into the anus in females and cloaca in males, present posteriorly.
- The respiratory system is absent and gaseous exchange occurs through the body surface.
- They do not possess a skeletal system, the pseudocoelomic fluid acts as a hydroskeleton.
- The excretory system is made up of canals. In nematodes, Renette cells are present, especially in marine nematodes. They are involved in osmoregulation. They excrete ammonia and urea.
- The nervous system comprises a nerve ring and nerve chords extending from it.
- Reproduction is sexual, fertilization is internal. Development is direct or indirect through the larval stage.
Aschelminthes Examples and Diseases
Common examples of aschelminth are:
Roundworm- Ascaris lumbricoides, Hookworm- Ancylostoma, Filarial worm- Wuchereria, Pinworm- Enterobius vermicularis, whipworm- Trichuris trichiura, etc.
They are known to cause various diseases in plants, animals and also humans. Some of the diseases are:
Ascariasis: It is caused by Ascaris lumbricoides in humans. It is very common in children. It causes abdominal pain, diarrhoea, vomiting.
Ancylostomiasis: It is caused due to hookworm infection in the small intestine. It causes anaemia. A large number of worms house the small intestine. They get stuck to the intestinal wall and suck blood causing anaemia.
Filariasis: It is caused by the roundworms. The lymphatic filariasis is caused by Wuchereria bancrofti, Brugia timori and Brugia malayi. It causes thickening of the skin and tissues present beneath the skin.
Loa loa causes subcutaneous filariasis. It infects eyes and skin.
Enterobiasis: It is caused by pinworm Enterobius vermicularis. It causes itching in anal area and causes sleeping discomfort.
Other diseases caused in the human being are trichuriasis, strongyloidiasis, trichinosis, etc.
There are many nematodes, which cause various plant diseases such as root-knot, root-lesion, cyst, burrowing, etc. They damage agricultural crops. Bacillus thuringiensis (Bt) produces insecticidal proteins (Cry and Cyt toxins), it is effective against nematodes too.
This was a brief note on Aschelminthes. Explore notes on Platyhelminthes and other important concepts related to NEET, only at BYJU’S.