Ascaris shows various parasitic adaptation due to parasitic mode of life.
(a) Morphological adaptations:
i. The body is long and cylindrical, pointed at both ends.
ii. The mouth is bounded by three lips which help the parasite to attach with mucous membrane of the host’s intestine.
iii. The parasite is devoid of locomotory organs as the parasite lives in the intestine where protection from enemies and food supply are ensured.
iv. The body wall of Ascaris is covered with cuticle, resistant to the digestive enzymes of the host.
(b) Anatomical adaptations:
i. The pharynx is muscular that facilitates ingestion of food by sucking action. There are no digestive glands.
ii. Sense organs are ill-developed, being found only on lips in the form of papillae.
iii. The digestive tract is simple without provision for storage, as there is constant supply of food.
(c) Physiological adaptations:
i. The body wall is covered with tough, thick and resistant cuticle, shields against the digestive enzymes of the host and antitoxins.
ii. Ingested food of this parasite is pre- digested, so that there are no elaborate digestive glands.
iii. The respiration is almost entirely anaerobic. Extremely low metabolic rate and anaerobic respiration enable the worm to live inside the host’s intestine, where the free oxygen is negligible.
iv. Reproductive system of Ascaris is well- developed and numerous eggs are produced to make up for the poor chances of the right host being reached.
v. The eggs are covered with resistant covering or chitinous shell which provide safety to the zygote and embryonated eggs from unfavourable environmental factors.
vi. The minute size and resistant nature of eggs make them to withstand prolonged dryness and cold. The minute size eggs afford far and wide dispersal of the parasite.