Parasitology,Animal Symbiosis or Association!!



The concept of parasitology is often misunderstood because of the complexity of the relationship between the parasite and its host.

Therefore, this section will define some of the general terminology often used in the description of organisms living together.


Many authors restrict the term symbiosis to relationship where in both partners are benifited.but here this term will be used in a wider sense, as was originally proposed by the German botanist Bary in 1879.


Sym: from the Greek/Latin meaning ‘with’

Bio: from the Greek/Latin meaning ‘to live’ or ‘living’.


A relationship where two organisms live together and at least one of the organisms benefits from the relationship.


According to the nature of symbiotic relationship or animal association it can be categorized into mutualism, commensalism and parasitism.


Mutualism refers to the relationship in which both are metabolically dependent on each other and both are benefited from the association.

New Picture (21)


  1. The fish lives its entire adult life among the tentacles of a sea anemone. Anemone fish do not get stung by the anemone as would most other fish so they get protection from predator. The fish often drop food scraps which the anemones can eat.MUTUALISM
  2. The Eel has a small fish cleaning between its teeth. The eel gets a clean mouth while the cleaner fish gets a nice meal.


  1. The humming bird moth is drinking the nectar of a flower. the flower gets pollinated(the moth brings pollen from other flowers)and the moth gets a tasty meal.



The term commensalism means ‘eating the same table’.

In commensalism, one partner or the commensal benefits from the association but the other or host is neither helped nor harmed.COMMENSALISM


  1. The tiny shrimp is riding along on the back of a sea cucumber while it crawls along a sandy bottom. The shrimp gets to travel around the protection of its much larger partner, and the sea cucumber does not seem to mind.
  2. The remora attaches to the shark and saves energy since it does not have to swim and gets to snack on the sharks kills. The shark does not get anythingCOMMENSALISM.
  3. The cattle walk around eating grass they stir up lots of insects. the egrets hang around and get a yummy meal of insects.COMMENSALISM


Parasitism means ‘eating from the table of another’.

Parasitism is an obligatory relationship between two hetero-specific organisms in which the parasite, usually the smaller partner, either harms its host or in some sense lives at the expense of the host.PARASITISM

The organism on which it lives is called parasite and the organism species which harbours the parasite is called host.

In animal kingdom several parasitism are recognized:

  • If a parasite lives on the surface of its host or superficially embedded in the host’s body surface, it is called ectoparasite.e.g. ticks, mites etc.
  • Parasite that live within the body of their host in locations such as tissues, body cavity, alimentary canal,liver,ling are known as endoparasite.
  • Organisms that do not absolutely depend on the parasitic mode of life, but are capable of adapting to it if placed in such relationship is known as facultative parasite.
  • Most parasite can not complete their life cycle without spending at least part of the time in a parasitic relationship. they are called obligatory parasite.


  1. Malaria is a disease caused by a parasite protozoan(Plasmodium sp).the protozoan is transferred effectively by mosquitoes (particularly anopheles).malaria infection kills 1 million people/year.
  2. The head louse (Pediculus) is an obligate ectoparasite of human. they are wingless insects. they spends their entire life on human scalp and feeding exclusively on human blood.body-lice

This is the basic concept of parasitology and symbiosis.

Thank you.


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