Extrapallial fluid

Allam, B., Paillard, C. and Auffret, M., Alterations in hemolymph and extrapallial fluid parameters in the Manila clam, Ruditapes philippinarum, challenged with the pathogen Vibrio tapetis. J. Invert. Pathol. 76, 63, 2000. 

A number of suggestions have been made that calcium may be transported because it is coupled to the movement of other ions or because it moves passively down an electrochemical gradient established by the movement of some other ions600. Thus, a sodium-induced potential has been found which was sufficient to account for the passive movement of calcium into the shell gland of the domestic fowl during egg shell formation. In the mollusc, the shell side of the mantle is normally positive relative to blood and a potential of this type would, of course, tend to move calcium away from the extrapallial fluid. A potential of this orientation could be produced by the movement of an anion into the animal (mollusc) and the low chloride concentration of the extrapallial fluid could be accounted for on this basis. 

The reaction of Eq. (4) would, of course, be capable of being catalyzed by carbonic anhydrase. Equation (5) represents the formation of mineral and the release of protons, whereas Eq. (6) indicates the removal of protons. Thus, although hydroxyl ion secretion may be the motivation force, the immediate result may be a slight fall in pH at the site of calcification. This is in keeping with the data, pointing out that the extrapallial fluid of molluscs is slightly more acidic than the blood. 

Crenshaw, M. A. The inorganic composition of molluscan extrapallial fluid. Biol. Bull. mar. bioL Lab., Woods Hole 143, 506 (1972)... 

The enzyme functions as a kind of chemical homeostaf by releasing calcium and carbonate to the extrapallial fluid from the reserves present in the mantle tissue. Because of the extreme sensitivity of the carbonate system to slight changes in pH (see p. 19, Fig. 14), carbonic anhydrase must operate in both directions in order to maintain a dynamic equilibrium between the bound and free calcium pools. 

The Golgi membraneous system also occupies a central position in mollusc calcification297. However, different from the coccolithophoridae, the actual CaC03 deposition does not take place inside the Golgi vesicles which are abundant in epithelial cells lining the surface of the outer mantle fold. Instead, the calcification site is an organic matrix released from the extrapallial fluid separating the mantle from the shell. 

Figure 5.17. Relationship between the partition coefficient for inner aragonite shell and coexisting extrapallial fluid of the marine mollusc, Pinctada furcata, and ionic radius of the elements. (After Speer, 1983.)...

Wada, K. and Fujinuki, T., 1976. Biomineralization in bivalve molluscs with emphasis on the chemical composition of the extrapallial fluid. In N. Watabe and K.M. Wilbur (Editors), The Mechanisms of Mineralization in the Invertebrates and Plants. University of South Carolina Press, Columbia, pp. 175—190. 

As this process occurs in supersaturated solution, the problem consists of suppressing the kinetics of random homogeneous nucleation in the extrapallial fluid wMle enhancing the kinetics of oriented nucleation on the organic protein surface. 

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