Urea and osmoregulation in the diamondback terrapin Malaclemys centrata centrata (Latreille).

The diamondback terrapin, Malaclemys centrata centrata (Latreille), is a thoroughly aquatic turtle living in salt and brackish marshes and estuaries. From its habitat, it is obvious that this animal has to contend with various osmotic conditions. Bentley, Bretz & Schmidt-Nielsen (1967) and just recently Dunson (1969) have already investigated the problem of the salt and water balance in that species. Our preliminary experiments have shown that inorganic ions are not the only effectors of the osmoregulation in the blood. This paper reports a comparison of the osmotic pressure of the blood and of the substances contributing to it in diamondback terrapins adapted to various salinities. The part played by the bladder has also been investigated in terms of modifications in the osmotic pressure and in the composition of the urine.