Carotenoid pigment occurring in algae. Isoln from Aphanizomenon flos-aqua: Tischer, Z. Physiol. Chem. 251, 109 (1938); 260, 257 (1939); from Paracentrotus lividus: Lederer, Compt. Rend. 201, 300 (1935); from Oscillatoria rubrescens: Heilbron, Lythgoe, J. Chem. Soc. 1936, 1376. Structure: Goodwin, Taha, Biochem. J. 47, 244 (1950); 48, 513 (1951); Goodwin, ibid. 63, 481 (1956); Ganguly et al., Arch. Biochem. Biophys. 60, 345 (1956). Synthesis: Akhtar, Weedon, J. Chem. Soc. 1958, 3986; 1959, 4058.