Notes on the osmotic and ionic regulation of some brachyuran crabs from Curaçao

Abstract

Data have been collected concerning total osmotic concentration and osmotic concentration of electrolytes in the blood of some marine, semi-terrestrial and terrestrial species of brachyuran crabs from Curaçao. In addition the renal and extra-renal transport of water and salts was measured.With increasing terrestrilization the various species show some distinct trends: a decrease of the osmotic concentration in the blood (mainly by a decrease in the amount of organic substances dissolved in the blood), an increase in the ability for osmotic and ionic regulation, an extension of the regulation ranges by a shift of the lower limits and a decrease of the salt flux through the gills.In the different species a relation between the concentration of organic substances and the osmotic value of the blood was found.The renal loss of water and salts is slight, contrary to the situation in brackish water animals. The (gross) extra-renal loss of salts tends to decrease in species better adapted to a terrestrial life. These losses are probably connected with the flow of blood through the gills and ventilation in the gills.The data bearing on the adaptations to a terrestrial environment have been compared with the adaptation to brackish water conditions. The evolutionary implications are indicated.