Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 71. (Budapest 1979)
Domokos, T.: On the morphological changes during ontogenesis of some Hungarian molluscs
value hjb is about 2.5. The data of the juvenile specimens (23 pieces) do not constitute a coherent picture if the study comprises the usual parameters. To absolutely ascertain the juvenile state is neither on the basis of size nor that of the set of teeth possible. Figs. 11 and 12 show clearly that even specimens of very big size can be edentate, or they have aborted teeth even if having strongly swollen lips. In the case of specimens having an abnormal set of teeth, the rudimentarity or the lack of a tooth on the pillar is most frequently the case. (In 97% of those with abnormal teeth.) The change of elongation, taking place in the course of the ontogenesis, can be illustrated by the functionality hjb —h (Figs. 11 and 12). The correlation is nearly linear. The greatest divergence of 13% can be observed in the juv. specimens at the value h — 4 (Fig. 12). The direction tangent of the straight line is approximately 0.22. The result is similar also in the case of fully developed specimens having mostly 3 teeth (Fig. 11). Here the divergence is max. 11%. The 3 teeth of Chondrula tridens appear probably not at the same time, consequently grow not at the same rate. The oral aperture is being built in the direction a-3-2-6 and thickens like an annual ring (Fig. 13). The tooth variations are given in Fig. 14. Tooth 1 (H 3 ) is camel-hump-like on the vault. It always appears as the first one and is only in 2.6% weak. Tooth 2 (C7 3 ) is L-shaped, its stem runs parallel to the edge of the oral aperture as far as the corner (b). Between the tooth and the corner, the oral aperture has a sharp edge and is slightly incised viewed from the side. It occurs that immediately below it the shell deepens to some millimetres. Tooth 3 (B) is hump-like at the bottom of the pillar. It is often lacking, it probably appears as the last one. The pillar itself cannot be regarded as a tooth. The order of tooth strength is: H z —G z —B. Having studied the parameters and the set of teeth, it is worth observing also the tendency of the shape of the oral aperture (Fig. 15). The angularity of the oral aperture of the young specimens is conspicuous. At the locus marked with an asterisk*, the oral aperture is nearly angular. Tooth 2 will eventually develop under this corner. At an older age, only a slight hollow in the shell and the depth of the previous seams might indicate this corner. Fig. 9. Relationship between A' (whorl number) and characteristic m 2 (mean): a = Habitat Baja, b = Habitat Csurgó. — Fig. 10. a= h — Fully developed specimens of Chondrula tridens (Szabadkígyós), b = j- (h = height of shell, b = breadth)
