. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CHITON ION AND WATER BALANCE 371 Osmotic permeability and chitons responding theoretically as osmometers The osmotic permeability, Pos, (calculated according to equation 1) was ± kg H^.O/kg animal X hr ' X unit osmolal concentration <h after 1 lir of exposure of chitons to 60%: SW ; the 2 hr value was ± hese P09 values did not differ significantly and were averaged and used to < .te the theoretical rate of weight change (equation 2) of chitons responding as if th perfect osmometers. M. muscosa does
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CHITON ION AND WATER BALANCE 371 Osmotic permeability and chitons responding theoretically as osmometers The osmotic permeability, Pos, (calculated according to equation 1) was ± kg H^.O/kg animal X hr ' X unit osmolal concentration <h after 1 lir of exposure of chitons to 60%: SW ; the 2 hr value was ± hese P09 values did not differ significantly and were averaged and used to < .te the theoretical rate of weight change (equation 2) of chitons responding as if th perfect osmometers. M. muscosa does not respond as an osmometer in hyposmotic SW. The per- cent increase of soft-part wet weight of chitons behaving as if they were simple Boyle-van't Hoff osmometers is : this value agrees well with the asymptotic value of calculated according to equation 2. The curve of chitons respond- ing as if they were osmometers and the curve of observed weight change begin to separate after approximately 1 hr. Therefore, mechanisms of volume control are coming into effect within 1 hr after transfer of chitons to 60% SW (Fig. 5). Muscle tissue water content With acclimation (2 days) to decreasing salinity the foot-muscle tissue of M. muscosa becomes increasingly hydrated. However, this tissue does not appear to respond as a Boyle-van't Hoff osmometer (P < , 60% SW ; P < 75% SW;F< , 125% SW) (Fig. 6). DISCUSSION The response of blood ions to changes in external salinity shows that the chiton Mopalia muscosa does not regulate the Na+ and Cl~ concentrations of its blood in either hyposmotic (60% SW) or hyperosmotic (125%. SW) media. Although the K+ and Mg-+ concentrations of the blood of 60% SW acclimated chitons are greater than the respective SW concentrations, these differences are small. The blood Ca2+ concentration of hyposmotically stressed chitons is hyper- regulated. Regulation of blood Ca2+ concentration has been shown in other hyposmotically stre
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
