Any member of a class of intensely colored pigments found in some algae that absorb light for photo­synthesis. Phycobilins are open-chain tetrapyrroles structurally related to mammalian bile pigments, and they are unique among photosynthetic pigments in being covalently bound to proteins (phycobiliproteins). In at least two groups of algae, phycobiliproteins are aggregated in a highly ordered protein complex called a phycobilisome.