34 



THE BIOLOGY OF MARINE ANIMALS 



acidity, etc.), but it has not yet been possible to relate these to the flotation 

 mechanism with any certainty (24). 



Among Metazoa osmotic adjustment has been studied in several species 

 with interesting results. Sipunculid worms such as GoJfingia (= Phascolo- 

 soma), Sipunculus and Dendrostoma tolerate a certain degree of osmotic 

 stress, adjusting to anisosmotic media. Golfingia gouldii survives exposure 

 to sea- water concentrations of 55 % and 160%, and Dendrostoma recovers 

 after loss of 43 % of body weight by desiccation. Superficially these animals 

 behave like osmometers, and on transferring to dilute or concentrated 



0/234567* 



Time (hours) 



Fig. 2.3. Changes in Body Weight of Golfingia gouldii 



when Injected with Dilute and Concentrated Sea Water 



Worms were injected at 0-2 hour with 12-17% body weight of sea water having the 



concentrations shown, after which they were immersed in normal sea water. Gradual 



decrease in weight about four hours after injecting concentrated sea water indicates 



salt loss. (From Adolph, 1936.) 



sea water they swell or shrink rapidly, reaching equilibrium in a day or 

 less. On returning the animals to normal sea water they tend to regain 

 original volume. Again, on injecting sea water of different concentrations, 

 animals subsequently alter in volume to a degree corresponding to the 

 concentrations of the fluids injected, i.e. when injected with hypertonic 

 solutions they swell and when injected with hypotonic solutions they 

 shrink, owing to osmotic transfer of water (Fig. 2.3). 



The integument of sipunculids (Golfingia, Dendrostoma) is semi- 

 permeable, permitting osmotic transfer of water in anisosmotic media. In 

 consequence, the body fluids remain isosmotic with the external medium 

 when the concentration of the latter is altered, i.e. osmotic adjustment 



