Phylum-Aschelminthes is considered a superphylum, which includes many phyla. The term Aschelminthes was first introduced by Grobben in 1910. Earlier in 1859, Gegenbour was named Nemathelminthes for this phylum. So, the Phylum Aschelminthes is also known as the phylum Nemathelminthis or the phylum Nematoda.
The Greek words
” Asko = bladder and Helminthes = worm”
There are about 15000 known species of this group. The animals are free-living and parasitic. The free-living forms are usually microscopic. They are worm-like cylindrical bilaterally symmetrical animals.
Aschelminthes are the group of unsegmented worm-like cylindrical organisms having pseudocoelom, epidermal nerve cords, the distinct digestive system with the mouth, and containing thick cuticular body wall.
Some common characteristics features of phylum Aschelminthes are –
1. The body is a long cylindrical unsegmented thread-like. They are length can vary from 1mm to 50 mm long.
2. Bilaterally symmetrical triploblastic body. The Organs are formed in the body.
3. There are pseudocoelom present in the body.
4. The alimentary canal is straight and complete with a distinct mouth.
5. Respiratory system and circulatory system are absent.
6. Body wall contains only longitudinal muscles.
7. Body covered with a layered cuticle.
8. The excretory system consists of a pair of lateral excretory ducts.
9. They have epidermal nerve cords with sense organs in the body.
10. They are dioecious with separate male and female forms.
11. Reproduction occurs by sexual methods.
12. Most of the animals are parasitic to other animals and plants. some forms are free-living in this phylum.
13. Some species of this phylum are parasitic on humans (Ascaris, Loa loa).
Identifying characters of Phylum-Aschelminthes:
1. Body structure: Their bodies are unsegmented and cylindrical.
2. Pseudocoelom: They have pseudocoelom in the body. There is no mesoderm in the body cavity.
3. Muscular system: Advanced types of the muscular system and consists of longitudinal and round muscle tissues.
4. Body membrane: Body covered with a layered cuticle.
5. Digestive system: In the phylum Aschelminthes, the digestive system is simple. A complete alimentary canal is present.
Some common genera of phylum Aschelminthes are Ascaris, Wuchereria, Nectonema, Ancylostoma, Gordius, Priapulus, Limnias, Chaetonota, etc.