Salt and Water Balance of the Spiny Lobster, Panulirus Argus: the Role of the Antennal Glands

Panulirus argus in full sea water differs from most other marine isosmotic decapods by regulating Cl− levels in the haemolymph slightly below those in sea water and by having haemolymph K+ levels similar to those in sea water. The species is typical in regulating haemolymph Na+ and Ca2+ above, and Mg2+ and SO42− below, sea-water levels of these ions. Its haemolymph Mg24−and SO42− concentrations are amongst the lowest reported in marine decapods. The antennal glands contribute to this regulation of Mg24− SO42− and Cl− by producing urine with markedly, and approximately equally, elevated Mg24− and SO42− levels, and slightly elevated Cl−levels, compared with those in the haemolymph. The antennal glands show a small tendency to conserve water.