Also found in: Dictionary, Thesaurus, Medical, Wikipedia.


(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.
..... Click the link for more information.
). 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.
..... Click the link for more information.
; 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
..... Click the link for more information.



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 ?
Write parasitism, commensalism, or mutualism next to each example.
One or more pseudoscorpions of the same species, in the green chamber of several nests of the same species of packrat would indicate that they actively seek, and remain in, this habitat to feed upon scavengers and detritivores (mostly mites)--this is commensalism.
Commensalism occurs when an animal or plant lives with, on, or in another to its own benefit but the relationship is neither parasitic nor mutualistic.
Rhesus commensalism in India: problems and prospects.
Part of this change must focus on the astounding degree of microbial diversity and ecological niches in the gut so that the body moves toward niche construction and beneficial colonization that leads to commensalism, symbiosis, and neurohormonal and immunological competence.
The actual nature of these associations is not well known, and is currently characterized as cases of commensalism, parasitism, or specialized egg predation (Berg & Gibson 1996).
The astounding degree of microbial diversity in the gut indicates a multitude of ecological niches, which are generated through the development of complex food webs (niche construction) whereby beneficial colonization leads to Commensalism, symbiosis, and immunological competence.
The lobsters feed on the sea urchins under which the juvenile abalones shelter, which effectively destroys the commensalism between abalone and urchin.
ABSTRACT Host specificity, extremely high prevalence and infection intensity, and easy sampling make the mantle-cavity ciliate Conchophthirus acuminatus a very convenient model to address numerous fundamental questions relating to symbiosis and commensalism.
In sum, traces on the brachiopod shells can either represent commensalism or parasitism.
No cases of CHV-1 infection have been documented in persons exposed to free-ranging macaques, in spite of a long history of human-macaque commensalism in Asia.
Contemporary human-macaque commensalism at each monkey temple is shaped by the behavioral characteristics of the particular monkey population as well as the community's unique geographic, social, religious, and economic factors.