BODY FLUIDS OF SOME CENTROPAGID COPEPODS - TOTAL CONCENTRATION AND AMOUNTS OF SODIUM AND MAGNESIUM

1. 1. Calamoecia salina, which inhabits athalassic saline waters and has a salinity range of 14-130%, is essentially poikilosmotic over the lower half of its range, but there is evidence of feeble hyperosmotic regulation towards the extreme low end. 2. 2. The marine brackish water species Centropages hamatus is completely poikilosmotic over the range 60-110% sea water, but strongly regulates magnesium (about 40% ambient concentration), and to a lesser extent sodium (slightly above ambient concentration). 3. 3. The body fluid of the fresh and brackish water species Limnocalanus macrurus has a freezing point depression of 0·36-0·38°C when in fresh water (Δ < 0·01°C). In the body fluid of this species, sodium is the dominant cation and magnesium is present only in very low concentrations. © 1969.