• An endoparasitic nematode in the small intestine of man and apes.

• Commonly known as Human Round worm.

• Body soft, cylindrical and pointed at both ends.

• Mouth at anterior tip guarded by three labial palps.

• Exhibits sexual dimorphism with female having long stout and straight posterior end.

• Male, short, thin with posterior end curved and hook like.

• Male has a cloacal aperture and penial setae, where as female has gonopore and anus.

• Presence of resistant cuticle, anti enzymes for protection from the host enzymes, muscular suctorial pharynx for sucking fluid food and high power of anaerobic respiration.