Eunotia serra Ehrenb.のサイズ減少に伴う殻形態の変化,特に波形の変化について

抄録

Eunotia serra is characterized by a dorsal margin with 4 to 20 or more undulations. How this variation depends on cell size reduction has not been clarified thoroughly. Fourteen parameters characterizing the valve outline of E. serra were defined based on the arc-constitutive model described earlier by the present authors. Each parameter was evaluated using 147 valves collectedfrom a pond in west-central Japan. The crests of the undulation arcs of a given wave precisely defined a large envelope arc, except for a few undulation arcs near each end. The radius ofthe envelope arc and the number of undulation arcs both showed high positive correlations with valve length. In contrast, valve width and the parameters constituting the undulation arc were not highly correlated with valve length. Valve length and arc number both showed an almost log-normal distribution, but valve width showed a normal distribution. The distance between a terminal arc center and the adjoining undulation arc center displayed an approximately uniform distribution within the range of 5% to 80% of the mean distance between undulation arcs. This suggests a process whereby the terminal arc approaches the adjacent undulation arc with every cell division, and finally unites with it; continuation of this process results in a decrease in the number of undulations as cell size reduction proceeds. Both the crests and troughs of undulation arcs near the center of the dorsal margin lay indifferently about the transapical axis; furthermore, the shape of the two terminal arc neighborhoods of a give n valve is mutually uncorrelated. The alignment of the train of undulation arcs along the dorsal valve margin is random and generally not symmetrical with respect to the transapical axis.