The coelomic fluid PCO2 levels were also influenced by the emersion temperature, and an increase in temperature leads to a rapid increase in PCO2. These changes in coelomic fluid PCO2 parallelled the changes in CO2 production in air. In echinoderms changes in pH are primarily influenced by the PCO2 of the body fluids . Here the increase in PCO2 leads to a decrease in pH by about 0.3 units in 15 and 25 °C. There was no change in pH in 5 °C and likewise there was no significant increase in coelomic fluid PCO2. However, there was probably also a concomitant rise in pH caused by the low temperature. Unlike the intertidal urchins P. miliaris and
E. esculentus there was no compensation for the acidosis. Generally echinoids have a better buffering ability than asteroids because the starfish can exchange CO2 through the bodywallmore efficiently, whereas the hard test of the urchins retards CO2 excretion