Spiders have blue blood due to the copper-based compound, hemocyanin, which aids in oxygenation.
Green-blooded skink of scincid lizard species has characteristic green blood and is native to Papua New Guinea and the Solomon Islands. The green hue is due to high concentrations of biliverdin, a toxic green bile pigment.
Sipuncula or peanut worms have purple blood due to the presence of the oxygen-binding protein called hemerythrin, which can be seen through their translucent skin.
Octopi have blue blood owing to the protein hemocyanin which contains copper instead of iron, as in haemoglobin. Hemocyanin carries oxygen to different parts of the octopus’ body and helps to survive in low-oxygen environments.
Sea cucumbers have yellow blood due to high concentrations of a vanadium-based pigment, vanabin. It does not aid in oxygenation and hence its presence is a mystery.
The blood of horseshoe crabs turns blue or blue-green when exposed to air due to the presence of a copper-based respiratory pigment called hemocyanin.