Cristaria plicata

The cockscomb pearl mussel, Cristaria plicata, lives in Japan and China. It produced the original rice-krispie pearls. They were small, irregular in shape, and had a wrinkled appearance. They were naturally white, but were frequently dyed. The mussels have thin shells and, when pearl cultivation was first attempted in China, were proved to be incapable of producing freshwater cultured pearls of high enough quality. 

Enterochrome-566 is a very similar pigment to helicorubin and is also found in gastropods as well as pelecypods. It has been purified from the gut fluid of Hyriopsis schlegelii, Cristaria plicata, Euhadra amaliae, and Euhardra sandai (286). Absorption peaks occur at 566, 530, and 430 nm in the reduced form and at 416 nm in the oxidized form. Its Ea is 200 mV at pH 6.4 and 150 mV at pH 7.8 (286). The biological function of both helicorubin and enterochrome-566 is not known. 

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