Haemoglobin from the marine invertebrate Arenicola marina (lugworm) is a large protein complex that can carry up to 156 oxygen molecules.Lugworms live on the sea shore. They are not very active and spend most of their time in their burrows covered by sea water.The primary function of lugworm haemoglobin is oxygen transport at high tide.The lugworm extracts as much oxygen as possible when covered with water as when the tide goes out it is no longer able to extract oxygen.The lugworm has a closed circulatory system. The extracellular haemoglobin has a high oxygen affinity and extremely high positive cooperativity in oxygen binding.The haemoglobin of the lugworm can transport 40 times more oxygen from the gills to tissues than human haemoglobin.