Osmolality and ions of the perivisceral coelomic fluid of the intertidal sea urchin Echinometra lucunter (Echinodermata: Echinoidea) upon salinity and ionic challenges

The intertidal sea-urchin Echinometra lucunter (Linnaeus, 1758) has been submitted to diluted sea water (SW) of salinity 25, or concentrated sea water of salinity 45. In addition, ionic challenges have been offered, supplementing 25 SW with Mg2+, Ca2+ or K+, until the concentration of each of these ions would reach the level of full-strength 35 SW (control). Perivisceral coelomic fluid has been sampled after six hours in these treatments for measurements of osmolality and concentrations of Na+, Cl-, Mg2+, Ca2+, and K+. Urchins have been further observed until five days. SW concentration (45) l...