File:American malacological bulletin (1988) (17968731418).jpg

Title: American malacological bulletin
Identifier: americanmal6719881990amer (find matches)
Year: 1983 (1980s)
Authors: American Malacological Union
Subjects: Mollusks; Mollusks
Publisher: (Hattiesburg, Miss. ?) : (American Malacological Union)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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Text Appearing Before Image:
Fig. 11. Spiral (S), pseudospiral (P) and rosette (R) microstructures are present in Area A in both caged and noncaged clams during cooler months (HFW = 23 jtm). (Tan Tiu, 1987). Details of the microstructure and function of the tubules are reported in a separate paper (Tan Tiu and Prezant, 1988). Some microstructures of the inner shell surface had low frequency of occurrences. An example of a microstruc- tural variant whose frequency of occurrence was low (less than 20% of total samples) and did not show distinct seasonal variation is shown in figure 14. Lamellae in figure 14 are ar- ranged in such a way that they resemble a pinwheel. Other examples of such variants are described by Tan Tiu (1987). B. WATER TEMPERATURE The temperature of the bottom water in the Leaf River was highest in August and lowest in January (Fig. 15). This was the only environmental variable that showed a distinct cyclic pattern. DISCUSSION The frequency of occurrence of Microstructure C in the outer shell layer and "well formed" lamellae in the transition zone of the inner shell layer of both caged and noncaged Cor- bicula fluminea exhibited seasonal variation. The time of oc- currence of these microstructures; however, were different. Frequency of occurrence of Microstructure C was inversely associated with bottom water temperature, while the presence of "well formed" lamellae in the transition zone was positively associated with bottom water temperature. Reticulate Microstructure observed in Corbicula fluminea is similar in appearance to that observed in Polymesoda caroliniana by Tan Tiu (1987, 1988). In both species, an increase in occurrence of Reticulate Microstruc- ture corresponded with a decrease in occurrence of other microstructural "types" in the areas involved. Several studies have suggested that valve closure results in calcium reab- sorption from the inner shell surface (Crenshaw and Neff,
Text Appearing After Image:
Fig. 12. Ultrastructure referred to as Reticulate Microstructure in the text (HFW = 21 /xm). Fig. 13. Highly eroded lamellae predominating in cooler months in Areas G to I (HFW = 19 ^m). Fig. 14. Pinwheel arrangement of laths (HFW = 21 /tm). 1969; Lutz and Rhoads, 1979; Akberali and Trueman, 1985). During valve closure under stressful or normal conditions, bivalves shift to an anaerobic metabolic pathway to generate ATP (Hochachka, 1980). The resulting acidic by-products,

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