Carotenoids in the muscle of Paphia amabillis (Veneridae) were investigated. Amarouciaxanthin 3-ester (1a) was found to be a major carotenoid along with amarouciaxanthin A (1b), fucoxanthinol 3-ester (2), peridininol 3'-ester (3), and a new C(37) skeletal carotenoid, named hydratopyrrhoxanthinol 3'-ester. This structure was determined to be 3'-acyloxy-3,5,6-trihydroxy-7',8'-didehydro-5,6-dihydro-12',13',20'-trinor-beta,beta-caroten-19,11-olide (4) by UV-vis, NMR, and FAB-MS spectral data. The absolute configuration of 4 was postulated to be (3S,5R,6R,3'R) on the bases of CD and ROESY data. The fatty acids esterified with hydratopyrrhoxanthinol were assigned as C22:6, C20:1, C20:4, C20:5, C18:0, C18:1, C17:0, C16:0, C16:1, and C14:0 on the basis of FAB-MS data.