Sea creatures with green, blue, purple and colourless blood

The colour of blood is determined by the protein responsible for transporting oxygen via the circulatory system to cells. That said, blood isn’t always red. Down in the oceans, green, blue and purple-blooded sea creatures are a dime a plenty. Here are some examples:

Green blood: tubeworm

tubeworms have green blood

Tubeworms have green blood due to the protein Chlorocruorin. The blood turns light green when it is deoxygenated but turns a darker green when oxygenated.

If you think that’s weird, wait till you hear this: tubeworms do not have a mouth, anus or digestive tract.

Instead of ‘eating’, food is manufactured by bacteria that live symbiotically inside their body. In return, the bacteria are provided with a safe haven and supplied with oxygen, carbon dioxide and hydrogen sulphide gathered by the worm’s ‘tentacles’.

Blue blood: octopus

octopus have blue blood

Like their cephalopod relatives such as squids and cuttlefish, the blue pigment in the octopus’ blood is derived from a copper-rich protein called Haemocyanin, which carries oxygen from the lungs to the bloodstream and then to the cells of their body.

This blue blood is nature’s way of helping them cope with the super low oxygen levels in the depths of the ocean.

Read about how octopuses are also some of the greatest masters of disguise.

Purple blood: peanut worm

Credits: Ria Tan, Wild Singapore
Credits: Ria Tan, Wild Singapore

Peanut worms have purple blood due to the protein Haemorythrin. But the blood is only purple when it is carrying oxygen; when deoxygenated, the blood is colourless.

Here’s something else that’s equally intriguing about these bottom burrowers: they have a long tube on their front end called the introvert which is attached to their body (or trunk). This introvert can be turned completely inside the trunk to send food particles to its mouth, or extended out of the trunk to collect food.

Do you know that peanut worms can be found on some of Singapore’s shores? In the past, they used to be so plentiful that they were collected and used as duck feed.

Colourless blood: ocellated icefish


These Antarctic Ocean-dwelling fish are the only vertebrate in the world with colourless blood, due to their lack of oxygen-carrying proteins. Instead of Haemoglobin, they use blood plasma to transport oxygen around their body.

The absence of Haemoglobin also results in white muscles, liver and gills, which are normally bright red. Their skin is also scale-less, which is thought to help it better absorb oxygen from the oxygen-rich waters of the Antarctic.

If you enjoy learning more about bizarre marine animals, come join us at our Halloween event Spooky Seas.

Spooky Seas at S.E.A. Aquarium, 1 – 31 Oct 2016

Online Exclusive: Family Bundle at S$68*
Two (2) S.E.A. Aquarium Adult Dated One-Day Passes
One (1) S.E.A. Aquarium Child Dated One-Day Pass


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