coelomic fluid

zoology

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June 24, 2026

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Coelomic fluid is a fluid found within the coelom, which is the body cavity between the body wall and the digestive tract in many animals, known as coelomates. In some simpler coelomates, like certain marine worms, coelomic fluid aids in circulation and may even transport oxygen, sometimes containing hemoglobin.12

In annelids, such as earthworms, coelomic fluid plays a crucial role in locomotion and osmoregulation. It also serves as a site for metabolic processes, temporary food storage, waste excretion, and gamete maturation. The composition of coelomic fluid varies; marine annelids' fluid is isosmotic with seawater, while freshwater species have mechanisms to regulate their internal fluid composition.3

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annelid
Tissues and fluids
The coelomic fluid of annelids plays a role in many important functions—e.g., locomotion and regulation of fluid transfer through the body wall (osmoregulation). Many metabolic processes occur in the coelom, which also serves as a site for temporary food storage, for excretion of nitrogen-containing wastes, and…
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The coelomic fluid of annelids plays a role in many important functions—e.g., locomotion and regulation of fluid transfer through the body wall (osmoregulation). Many metabolic processes occur in the coelom, which also serves as a site for temporary food storage, for excretion of nitrogen-containing wastes, and…
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respiratory system
Gills of invertebrates
…supplemented by extensions of the coelomic, or body-fluid, cavity into thin-walled “gills” or dermal branchiae that bring the coelomic fluid into close contact with seawater. Sea cucumbers (Holothuroidea), soft-bodied, sausage-shaped echinoderms that carry on some respiration through their oral tentacles, which correspond to tube feet, also have an elaborate “respiratory…
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…supplemented by extensions of the coelomic, or body-fluid, cavity into thin-walled “gills” or dermal branchiae that bring the coelomic fluid into close contact with seawater. Sea cucumbers (Holothuroidea), soft-bodied, sausage-shaped echinoderms that carry on some respiration through their oral tentacles, which correspond to tube feet, also have an elaborate “respiratory…
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