ABSTRACT
Two Interrelated oxygen-providing levels are supposed to be developed in echinoderms in the course of their evolution. The first level is the external, one is with sea water which can have considerable variations in dissolved oxygen. Diffusing from the environment to the ambulacral system, oxygen fuels the high ATP output, locomotion and, to some extent, active metabolism of the animals. The second level is the internal one the stable, reduced oxygen content in the coelomic liquid that maintains the vitality of the internal tissues. High concentration of lactste as the end product of the anaerobic metabolism is observed in the internal tissues. It provides sufficient energy yield to support basal metabolism when the environmental oxygen concentration is reduced. Physiological, biochemical and ethological strategies of adaptation of echinoderms to environmental factors are aimed at efficient uptake of molecular oxygen from the sea water, The mechanisms determining respiration homeostasis of echinoderms promote flourishing of many echinoderm species under unstable oxygen conditions in the upper sublittoral zone of the sea.
