Abstract 1. 1. The rate of oxygen consumption of this burrowing spatangoid was measured for individuals ranging in size from 3-month old 2.5-mm long juveniles to 39-mm long adults. 2. 2. The decrease in the rate of oxygen consumption/dry weight with increasing body size is greater among mature adults than among juveniles because the increase in aerobic tissue (primarily the test) with body size is less than the increase in anaerobic tissues (mainly the gonads). 3. 3. The rate of oxygen consumption/ash-free dry weight decreased more slowly with increasing body size because of the increase in the level of inorganic material. 4. 4. Replacement of the common fresh weight or dry weight specific oxygen consumption by a more synthetic value calculated from ash-free dry weight specific oxygen consumption measurements, to annulate the body-size effect, is proposed for interspecific comparison over a wide range of body size, taking into account parameters such as temperature.