It is made up of 2 Greek words, nema = thread & edios = form
Characters:
Body form:
They have elongated, cylindrical and unsegmented body like threads, so often called thread worms.Habitat:
Most of them are parasites while few are free living found in soil or water.Cellularity:
They are multicellular organisms with organ-system grade of body organization.Coelom:
They are pseudocoelomates.Nutrition:
They exhibit parasitic or holozoic modes of nutrition.Digestive system:
Digestion is extracellular.Alimentary canal:
Alimentary canal is complete and straight with mouth, pharynx, intestine and anus.Excretion:
Excretory system is absent. Gaseous exchange occurs through the general body surface.Circulatory system:
Blood vascular system is absent. Transport of materials occurs with the help of hydrolymph or pseudocoelomic fluid.Reproduction:
They are usually dioceious i.e. sexes are separate with sexual dimorphism. No asexual reproduction occurs.Fertilization:
It is internal and cross.Nervous system:
Nervous system consists of a nerve ring and the anterior part of the alimentary canal with longitudinal nerve cords.Germ layers:
They are triploblastic.Segmentation:
Body is unsegmented but maybe wrinkles.Cephalsation:
Body lacks the distinct head. However, mouth is present in the anterior system.Sensory Organs:
Amphids and phasmids are the sensory organs present in them.Development:
Development is direct without any larval form.
On the basis of presence or absence of Phasmids (caudal sensory organ), phylum nematode is futher classified as :
1. Class 1. Aphasmidia:
- Most of them are free living forms.
- Phasmids are present.
- Amphids are of various types.
- Excretory organs are either reduced or absent E.g. Enoplus, Mermis etc.
2. Class 2. Phasmidia:
- Most of them are parasitic forms.
- Phasmids are present.
- Amphids are pore like.
- Excretory organs are developed with paired lateral canals. E.g. Ascarics lumbricoidesetc.
Top comments (0)