The blood of a cuttlefish is an unusual shade of green-blue because it uses the copper-containing protein haemocyanin to carry oxygen instead of the red , iron-containing protein haemoglobin found in vertebrates ' blood .
The blood of a cuttlefish is an unusual shade of green-blue because it uses the copper-containing protein haemocyanin to carry oxygen instead of the red iron-containing protein haemoglobin that is found in vertebrates .