ABSTRACT
Oxygen consumption 
, haemoglobin oxygen saturation level 
and pH 
in prebranchial blood were measured in lugworms experimentally confined in sea water at 15 ·C. Total blood flow through the gills 
was estimated. For seawater oxygen partial pressure 
between 120 and 150 Torr, 
, and 
were high and nearly constant. For 
< 120 Torr, 
fell quickly, 
progressively dropped, and metabolism remained aerobic at the expense of the prebranchial blood oxygen store. For 
< Torr, 
and 
values were extremely low, and the low 
and the modified buffer power of the surrounding sea water showed that anaerobic metabolism was occurring. Changes in respiratory gas exchanges and metabolism during the tidal cycle are deduced from the comparison of these results with data obtained in the field.
