On the diverse colours of Nereis diversicolor

The variable colour of Nereis diversicolor is due to variations in the proportion of green, orange and brown pigments. The orange and brown pigments are mainly carotenoids; the green colour is due to biliverdin. Phaeophorbide-a and coproporphyrin III also occur, but both these pigments may be restricted to the gut wall; biliverdin occurs both in the wall of the gut, and in the epidermis and coelomic cells. The biliverdin is formed by the breakdown of the haemoglobin of the blood. Haemoglobin-breakdown takes place in the epidermis on the dorsal side of the body, in the epithelial tissue surrounding the proboscis and in the pygidium. Granules of biliverdin are probably removed by the coelomic cells and conveyed to the gut into which they are excreted. In ripe males, and in females during and after spawning, phagocytosis of the tissues is accompanied by an increased haemoglobin-breakdown with a corresponding accumulation of biliverdin in the body. The green appearance is due not only to an increased amount of biliverdin, but also to a complete extraction of carotenoids from the body-wall.