Table 12. — Distinctive properties of principal mineral forms of calcium carbonate found in invertebrates ' 



I From the data published by Prenant, 1927. 



an important role in the formation of calcium 

 deposits in molluscan shells has been advanced by 

 Stolkowski (1951). According to this theory the 

 enzyme exerts its effect by orienting the calcium 

 carbonate molecules in the aragonite crystal 

 lattice. The action of carbonic anhydrase in this 

 admittedly very complex process is not, liowever, 

 satisfactorily explained and should be more 

 thoroughly investigated before its role in the 

 formation of aragonite or calcite in mollusk shells 

 is definitely established. In its present state the 

 hypothesis fails to explain the existence of shells 

 in which both aragonite and calcite are present. 

 Recently Stenzel (1963) reported that in the shells 

 of C. virginica aragonite covers the areas of attacli- 

 ment of the adductor muscle, tlie inipiiiit of 

 Quenstedt's muscle, and is found in the ligament. 



Another explanation of the formation of the 

 less stable aragonite instead of calcite suggests 

 that strontium and magnesium carbonates in- 

 fluence the formation of aragonite in shell. Some 

 support to this idea is found in the fact that in 

 vitro the crystallization of aragonite is facilitated 

 by strontium and lead salts. This observation 

 made by Prenant (1924) apparently influenced 

 Trueman's (1942) hypothesis that strontium, 

 magnesium, and probably other salts found in 

 living mollusks influence the crystallization of 

 aragonite. 



That there may be some correlation between 

 the predominance of the particular mineralogical 

 form of calcium carbonate and the temperature 

 of the surrounding water has recently been 

 suggested by some geologists. Through quanti- 

 tative X-ray analysis of shells they have demon- 

 strated that in certain polyclad worms (Serpulidae) 

 and in some gastropods and pelecypods {Mytilus, 

 Vohella, Pinctada, Anomia, and others) the con- 

 centration of aragonite in shells increases with 

 increasing temperatm'es (Epstein and Lowenstam, 

 1953; Lowenstam, 1954). In Mytihts, for in- 

 stance, only the sliells of warm water species are 

 composed entirely of aragonite, whereas those 



from colder waters contain varying amounts of 

 both calcite and aragonite. This interesting 

 ecological observation does not, however, provide 

 a clue to the nature of the biochemical processes 

 which control the predominance of one or another 

 crystallization system. 



RATE OF CALCIFICATION 



The calcification rate of the left valve of C. 

 virginica is significantly higher than that of the 

 right one, as can be readily seen by examining 

 newly formed shells. The calcareous material 

 deposited by the left mantle is thicker and 

 heavier than that deposited during the same time 

 by the right mantle (Galtsofl', 1955). I made 

 the following observations on shell growth rate of 

 adult C. virginica. After the new growth of shell 

 along the valve edge was carefully removed the 

 oysters were placed in tanks abundantly supplied 

 with running sea water. About 2 months later 

 the areas of newly deposited shells on each valve 

 were measured with a planiineter, carefully re- 

 moved from the shell, rinsed in distilled water, 

 dried in air, and weighed. The results are 

 summarized in table 13. In every case the 

 amount of calcified material deposited over a 

 unit of area was considerably greater on the left 



T.^BLE 13. — Areas of new yroivth and rate of deposition of 

 shell material by C. virginica in mg. per day per C7n.' 

 during April to June 1934, ^Voods Hole, Mass. 



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