[Specific Features of Linear Growth Influencing Morphometric Parameters of the Shell in Margaritifera margaritifera...

Interdependence of parameters of shell growth in length and height during ontogeny has been studied in the freshwater pearl mussel M. margaritifera. It has been shown that the results of determining the height-to-length ratio depend on at least two factors: shell corrosion in the apical (umbo) zone and regular, rhythmic deviation of this ratio from values expected from linear regression equation. The first factor may be taken into account by applying an individual correction for each specimen, thereby making the ratio of linear dimensions independent of mussel age and size. The calculation error caused by biological rhythms may be reduced by measuring the greatest possible number of annual rings (> or = 18). Factors accounting for alternation between periods of prevalent shell growth in length or in height are discussed.