Bivalve hemocyanins--a comparison with other molluscan hemocyanins.

1. The hemocyanins of the protobranch bivalves Yoldia thraciaeformis, Yoldia limatula and Acila castrensis have absorption spectra similar to other hemocyanins. 2. Hemocyanins from all three bivalves appear as six-tiered cylinders in the electron microscope (30-32 nm in diameter by 34-38 nm in height). Yoldia thraciaeformis and A. castrensis hemocyanins tend to dissociate to three-tiered half molecules with polar images and also to associate into long tubular polymers. 3. Yoldia thraciaeformis and A. castrensis hemocyanins chromatograph on Sepharose 4B gel close to gastropod hemocyanin (Mr = 9 x 10(6] rather than chiton hemocyanin (Mr = 4 x 10(6]. 4. Hemocyanins from all three vivalves have subunits with electrophoretic mobilities similar to gastropod and polyplacophoran hemocyanin subunits and slower than octopodan hemocyanin subunits. 5. These similarities between bivalve and gastropod hemocyanins are consistent with the hypothesis that bivalves and gastropods have shared a common ancestor.