The oxygen transport characteristics of lugworm blood were studied over a range of temperature and pH values encompassing tidal and seasonally dependent measurements from worm burrows. The blood showed a small carbon dioxide Bohr effect (?log P50/?pH = ‐0.14 to ‐0.06), contrasting with the known pH sensitivity of blood in the European lugworm,Arenicola marina.The exothermic nature of oxygen binding was greater for the New Zealand species (?H ≈ ‐36 kJ mol‐1) but less than that shown for most other invertebrates. The CO2‐Bohr effect was indistinguishable from the fixed acid Bohr effect, suggesting a lack of specific CO2binding by the blood. Worms acclimated at 15 and 25°C did not show thermal compensation of in vitro blood oxygenation; these data are discussed in relation to the temperature induced Bohr effect inA. marina.