A detailed identification of qualitative composition of tissue carotenoids in the Black-Sea dominant molluscs Mytilus galloprovincialis Lam., Crassostrea gigas Th., Anadara inaequivalvis Br., Rapana venosa Val. accounting for peculiarities of their ecology has been performed using several analytical methods such as LC, CC, HPLC, qualitative reactions for certain chemical groups, the visible spectral analysis, FAB MS and H'-NMR. Twenty (>99% of the total), six (>80% of the total), six (>95% of the total), and nine carotenoids (>85% of the total) have been identified in bodies of M. galloprovincialis, C. gigas, A. inaequivalvis, and R. venosa, respectively. It has been established that the main carotenoid-accumulating organ is the hepatopancreas in sedentary and sessile forms of bivalve filter feeders and the foot in mobile ones. A core group of carotenoid pigments has been identified for each type of the molluscs. It has been found that alloxanthin, diatoxanthin, and pectenol A are common for the bivalve tissues. The species-specific groups of pigments have been identified as crassostreaxanthins A and B in C. gigas, mytiloxanthin and heteroxanthin in M. galloprovincialis, and trans- and 9-cis-pectenolone in A. inaequivalvis. The pathways of the carotenoid transformation in the phytoplankton -> filter-feeder molluscs food chain have been proposed. For the first time, three novel 19'-hexanoyloxy-carotenoids, namely 19'-hexanoyloxyhalocynthiaxanthin, 19'-hexanoyloxycrassostreaxanthin A, and 19'-hexanoyloxyallenicmytiloxanthin, have been identified in minor amounts in the tissues of M. galloprovincialis. A new transformation scheme for the compounds of this series has been proposed. The scheme of metabolic transformation of carotenoids in the shellfish-filter -> shellfish-predator food system by the example of the main carotenoids of the bivalves and R. venosa has been refined. One of the routes is based on the accumulation of alloxanthin as the most abundant diacetylenic carotenoid, with all its isomeric and ester diatoxyforms, in the tissues of the predator. Another one is based on the transformation of diatoxanthin into 7, 8-didehydroasthaxanthin.
