Further Studies on Ionic Regulation in Marine Invertebrates

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Abstract
1. The blood or coelomic fluid has been analysed in sixteen marine invertebrates to determine the amount of ionic regulation. 2. Little regulation is shown by Holothuria and the bivalves Ostrea and Mytilus except in potassium. The bivalves accumulate potassium (up to 135% of the concentration in sea water), and Mytilus galloprovincialis accumulates sulphate (to 120%), an unusual feature. 3. The nudibranch Archidoris accumulates potassium (128%), calcium (132%) and magnesium (107%), while the sipunculid Phascolosoma has lower magnesium (69%) and sulphate (91%) but higher sodium (104%). 4. The cephalopod Sepia regulates all its ions except magnesium, range of values (expressed as percentage of concentration in dialysed plasma) being Na 92-94%, K 193-223%, Ca 84-97%, Mg 97-100%, Cl 105-106%, SO4 17-29%. Protein averages 109 g./l. in the three specimens analysed. Fluid from the renal sacs contains high concentrations of NH4+ ions, in two specimens 146 and 59 m.equiv./kg. water, and differs from a plasma ultrafiltrate in the concentration of all other ions. 5. The vitreous humour in the cephalopod eye is a clear protein-free fluid, isosmotic with the plasma within 1% but having ionic concentrations markedly different from those of a plasma ultrafiltrate or dialysate. In Sepia, Loligo and Eledone magnesium may be only 10-20% and sodium over 115% of the concentrations in a dialysate of the plasma. In one specimen of Sepia the aqueous fluid in front of the lens largely resembled sea water except for lower concentrations of magnesium and sulphate. 6. Among the decapod and stomatopod Crustacea regulation of all ions exists, ranges in eight species being Na 97-111%, K 120-156%, Ca 84-137%, Mg 32-99%, Cl 96-103%, SO4 53-135%. Species of Portunus and Eupagurus show more regulation than Dromia and the spider-crabs Maia and Hyas. Regulation in the stomatopod Squilla resembles that in the portunid family. In the grapsoid crab Pachygrapsus each ion in the plasma is maintained below its equilibrium value: Na 94%, K 95%, Ca 92%, Mg 24%, Cl 87%, SO4 46%; total ions 1.163g. ions/kg. water compared with 1.353 in sea water. 7. In sixteen crustaceans an inverse relationship exists between the degree of activity and the magnesium content of the blood: the more active ones have low values of magnesium.

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