Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 71. (Budapest 1979)

Domokos, T.: On the morphological changes during ontogenesis of some Hungarian molluscs

Reality differs from the model in the following points: 1. In the plane of the axis, a dislocation of small extent and of varied dimensions have to be reckoned with. 2. Sections of the whorls are not circular but reniform. 3. The plane of the whorls diaphragm is not parallel to the axis. The position, the form of the oral aperture reveals much on the shell-carrying, and, in an indirect way, on the habit of life of the animal (WAGNER 1928, GEYER 1929, ROTARIDES 1935-1936) (Fig. 3). In the case of the Planorbidae the plane of the oral aperture intersects the shell axis (the outer and the upper lips run forward). A comparative study of the two sides of the shell gives an interesting result. Fig. 4. shows the results derived after measuring both sides of the Planorbarius corneus in photographic way. The analysis was made with the assumption of a logarithmic spiral. The growth is in both cases logarithmic, as the functionality log r —K is linear. The rate of growth, however, is varying. At the top it is of a greater rate, although it starts from a lower value. This can be well seen also when studying the curve r—K (Fig. 4). The angle of inclination (S) of the diaphragm between the whorls can be determined by measuring AB and AC (Fig. 5). (AC by calculating the difference of values obtained photographically AB by direct measuring.) I have also studied how the rotundity index of the mouth increases during ontogenesis. The study was performed for ecological purposes. It is interesting that the index of the specimens collected in salt puddles Fig. 1. Frequency curves: 1 = live and dead specimens (broken + continuous line), 2 = dead specimens, 3 = live specimens. — Fig. 2. Frequency curves of dead specimens. — Fig. 3. Characteristics of Planorbidae: w = breadth of mouth, h = height of mouth. — Fig. 4. Relationship between K (whorl number) and radius, log r of spiral Planorbarius corneus: at top "a" curve, "b" line; at bottom "c" curve, "d" line