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Observations on Osmotic Relationships in the Holothurian Opheodesoma spectabilis

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Title:Observations on Osmotic Relationships in the Holothurian Opheodesoma spectabilis
Authors:Freeman, Paul J.
Date Issued:Jan 1966
Publisher:University of Hawai'i Press
Citation:Freeman PJ. 1966. Observations on osmotic relationships in the holothurian Opheodesoma spectabilis. Pac Sci 20(1): 60-69.
Abstract:The means whereby Opheodesoma spectabilis, a holothurian confined
to the quiet waters of Hawaii, can tolerate a dilution of 80% sea water were investigated.
The animal is notable for the ratio of coelomic to tissue fluid, about 4:1.
Weight changes, osmometry, titrations, and sodium analyses on fluids before and
after immersion of the animal in diluted sea water were some of the methods
The animal was found to reduce its content of coelomic fluid when placed in
dilute sea water for 24 hr. There is no rhythmic circulation or pumping of fluids.
Water exchange and regulation of volume are by way of mouth and anus, as the
body wall proved to be impermeable to water. Soluble salts of body fluids in both
starved and feeding animals are below the concentrations found in sea water; but
in feeding specimens, the coelomic fluid demonstrated osmotic activity approaching
that of sea water.
It is suggested that tolerance to fresh water by the tissues is incidental, and
derives from (1) the slow replacement of the comparatively large volume of coelomic
fluid with environmental water, and (2) the habit of steady ingestion of variable
quantities of organic material, leading to changing levels of digestive end-products
in the coelomic fluid. Cells within the small volume of tissue fluid exchanging with
the coelomic compartment can tolerate and have time to equilibrate with a wide
range of concentrations, out of adaptive necessity. Volume regulation occurs in the
gradual exchange between coelomic and environmental water to further advance
osmotic equilibrium.
Appears in Collections: Pacific Science Volume 20, Number 1, 1966

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