Red Blood Cell Oxygen Binding in Capitellid Polychaetes.

The oxygen equilibrium properties of red blood cells that circulate in the coelomic cavities of 10 morphologically similar capitellid polychaetes are generally species specific. Appreciable differences in oxygen affinity distinguish most of the species and, in several instances, cooperativity differs as well. The range of oxygen affinities is far greater than in the other closely related polychaetes examined to date. We suggest that the differences may prove to be adaptations to thermal properties of the environment, body size, or both.