A super-carbon-chain compound, symbiopolyol (1a), was isolated from a symbiotic dinoflagellate of the jellyfish Mastigias papua. Although a direct comparison between symbiopolyol (1a) and lingshuiol B has not been completed, symbiopolyol (1a) is suggested to be the enantiomer of lingshuiol B. The structure of 1a, including its partial relative configuration, was elucidated on the basis of interpretation of spectroscopic data and chemical transformations. This compound exhibited significant inhibitory activity against the expression of VCAM-1 in human umbilical vein endothelial cells (HUVEC).