Kingdom: Animalia
Phylum:  Nematoda
Commonly known as:  Roundworm
Commonly found in: Marine, freshwater, and terrestrial environments.
Mobility:  S-shaped motility

Nematodes are transparent, size ranges from millimetre to centimeter that is easily visible to human eye, elongated cylindrical in shape without segmentation and outer layer is made of elastic cuticle which sheds four times during its life form.They are parasitic in nature, thus feeding on algae, bacteria, fungi, other nematodes, animals, plants and play an important role in nutrient recycling, decomposition of waste materials. Birds carry nematodes from one ecosystem to other during their annual migration. They mostly inhabit in moist areas or in body fluids by host during parasitic interactions. They move by forming S-shaped curves by maintaining high internal body fluid pressure and tough elastic nature of cuticle. They act as bio-indicators and if they are absent in aquatic system it indicates the water is polluted or some toxic substance is present. Enterobacteriaceae is usually microflora in the guts of nematodes, thus presence of nematodes in drinking water is not safe. Also the presence of nematodes in water can be checked by observing the turbidity, higher the turbidity more are the number of nematodes present ^[ .