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(kəmĕn`səlĭz'əm), relationship between members of two different species of organisms in which one individual is usually only slightly benefited, while the other member is not affected at all by the relationship. For example, some flatworms live attached to the gills of the horseshoe crab, obtaining bits of food from the crab's meals; the crab is apparently unaffected. In many cases commensalism cannot be distinguished from parasitism (see parasiteparasite,
plant or animal that at some stage of its existence obtains its nourishment from another living organism called the host. Parasites may or may not harm the host, but they never benefit it.
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). See also competitioncompetition,
in biology, relationship between members of the same or different species in which individuals are adversely affected by those having the same living requirements, such as food or space. Intraspecific competition, i.e.
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; symbiosissymbiosis
, the habitual living together of organisms of different species. The term is usually restricted to a dependent relationship that is beneficial to both participants (also called mutualism) but may be extended to include parasitism, in which the parasite depends upon
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inquilinism, the cohabitation of animals of different species, whereby one (the commensal) benefits permanently or temporarily from the other without causing the latter any damage.

A commensal may use the other organism for protection or transportation, or it may take advantage of the latter’s food supply. Characteristically commensal animals are divided into three groups, according to the character of the interrelationship:

(1) The commensal limits itself to the use of the food of the organism of the other species; for example, the annelid Nereis lives in the coils of the shell occupied by the hermit crab and eats the crab’s leftover food.

(2) The commensal attaches itself, temporarily or permanently, to the body of the other species, in this case called the host; for example, the remora attaches itself by the dorsal fin, which has developed into a sucker, to sharks and other large fishes and uses them for transportation; certain marine hydroids settle on the skin of fish and feed on their excrement; and certain crustaceans (such as acorn barnacles) live on the skin of whales and the shells of mollusks.

(3) The commensal settles in the viscera of the host; for example, the infusorians of subclass Protociliata live in the rectum of frogs, and certain flagellates live in the intestines of mammals.

Parasitism may have originated evolutionarily from commensalism in which the commensal settles in the organs of the host. Symbiosis may also have been an elaboration of commensalism. However, commensalism is not an obligatory transitional step to parasitism or symbiosis; these forms of interrelationship may have originated independently of commensalism in the historical development of the given organisms.


An interspecific, symbiotic relationship in which two different species are associated, wherein one is benefited and the other neither benefited nor harmed.
References in periodicals archive ?
In SOS algorithm, three phases of the search are performed mimicking the three symbiotic interactions namely mutualism, commensalism, and parasitism phase.
This includes the phenomena of commensalism (an association in which one symbiont benefits and the other neither benefits nor is harmed); parasitism (an association in which one benefits and the other is harmed); and mutualism (an association in which both symbionts benefit).
Commensalism adaptation and gen flow mosquitoes of the Culex pipiens complex in different habitats.
We report here on recent observations of simultaneous parasitism and predation effects on breeding seabirds, including the effects of competition and commensalism among predators, as an example of interacting stressors caused by ongoing climate change.
Ponds are ecosystems in which microorganisms and shrimp are engaged in a variety of ecological interactions, from competition and predation to pathogenesis and commensalism (Moriarty, 1997).
The recent agreement that fits a relationship of commensalism with Sudan have raised doubts among the majority of the people, with some introspecting if late Dr.
Commensalism between Corynoneura Winnertz (Diptera, Chironomidae) and Corydalus Latreille (Megaloptera, Corydalidae) in Southeastern Brazil.
In this context, CFES, GAC and all geoscience associations will have to continuously scan the evolving economic and societal landscape that surrounds them, find the appropriate 'niches' in the crowded habitat, and maintain a balanced, healthy 'ecosystem' relationship where commensalism (two-way, where one benefits without hurting the other) or mutualism (both benefit) are the rule.
After that Phanikumar, Seshagirirao and Pattabhiramacharyulu [13] studied the commensalism of two species with limited resources.