Abstract
1. Heterocypris incongruens contains at least three different types of pigment: carotenoids, a pteridine, and a bilin. Haemoglobin and other haem pigments appear to be lacking in this species. 2. Astaxanthin and β-carotene are the only carotenoids found, even when the ostracod is feeding on algae containing abundant xanthophylls of various types. 3. A yellow pteridine, which rapidily decolorizes after extraction, is widespread in the body of the ostracod, but not in its eggs. It is suggested that this substance may play a part in the intermediate metabolism of the ostracod when in anaerobic conditions. Heterocypris can live and reproduce in anaerobic conditions for at least 2 weeks. 4. Biladiene pigments accumulate in the gut wall when the ostracod feeds on blue-green algae. These pigments can be made to disappear from the gut wall by restricting the diet to green algae, then made to reappear when a blue-green alga is given as food.