A group of arthropods have no red blood cells. Hence they have a different 'source' (a respiratory pigment) to transport oxygen. This source is dissolved in the plasma of the organism's body. Identify the 'source' that helps in transporting oxygen.

The correct option is A Haemocyanin
The respiratory pigment that is most commonly found in arthropods is hemocyanin. Majority of crustaceans and centipedes have hemocyanin. It is found dissolved in the plasma of the organism’s body and transports oxygen throughout the body.

So, the correct answer is 'Haemocyanin'.