Some Osmotic Adaptations of Onuphis Magna (Polychaeta: Onuphidae)
Abstract:Microcryoscopic comparisons of freezing-point depressions in paired coelomic fluid and diluted sea-water samples show that Onuphis magna is a hyperosmotic regulator with an osmoregulation curve exhibiting a distinct leveling at 245-265 mM/1 NaCl concentrations; but Onuphis fails to survive at the greatest dilutions (less than 25 per cent sea water or 4.5‰ Cl), indicating a probable lack of tolerance to dilution in its tissues.
This species exhibits a pattern of volume regulation similar to that previously published for O. erimita, regaining near normal body volume within three hours after experimental dilution. A lack of increase in respiration during volume regulation, in disagreement with published reports for Neanthes, is apparent from a limited number of observations on Onuphis. Volume regulation occurs mainly in the middle body region, the anteriormost segments, which have either reduced or no nephridia, remaining conspicuously swollen. In nature these segments may serve as a plug for the tube to restrict further water influx into the lower tube and burrow. In addition to differential swelling, posterior coelomic fluids are maintained in a distinctly darker and more viscous state than those of the most anterior segments under hyposaline conditions. The significance of such differential phenomena in the osmoregulation of this species is discussed.
Document Type: Research Article
Publication date: 1965-12-01
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