In the top shell, Turbo cornutus, the effects of hypoxia on the oxygen uptake at the gill and the oxygen transport with the blood were examined. The efficiency of the oxygen uptake at the gill was higher than those of the octopus and the cuttlefish； it is almost equal to those of the active fishes. However, the oxygen capacity of the blood was remarkably smaller than those of cephalopod and active fish species. Conversely, the cardiac output was markedly larger than those of cephalopod and active fish. These results suggested that the top shell should maintained both the ventilation volume and the cardiac output in the high level owing to the low oxygen capacity of blood in order to keep the high metabolic rate. Under hypoxia, the top shell increased the ventilation volume, the efficiency of the oxygen uptake at the gill and the cardiac output were increased and the oxygen utilization was almost constantly maintained.