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

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

The more obtuse the corner marked* is, the deeper the seams will be. I presume that the rounding of the mouth is probably caused by the gradual growing of the body of the tensile force of the animal. The interrelation shell-body is constantly changing in the course of the ontogenesis. B i V a 1 V i a: Unio sp. I believe that an analysis of the functionality N-h should be applied in order to follow the form changes of the shells (Figs. 16-17) (DOMOKOS 1979). A great number of "annual rings" found on a single specimen offer a good possibility, even in spite of the errors resulting from h and from the difficult reproducibility of m to the cognition of the curve of the above functionality. This paper demonstrates the essence of the analysis on the example of only some specimens taken at random. As it can be seen also in Fig. 17, the value N of the three Unio species found in the same biota increases considerably at the beginning, then, with the further increase of h its increase becomes slower. Studying the growth rate of the particular species, a considerable difference between the process of the elongation of Unio pictorum and that of U. crassus is experienced. When comparing specimens originating from various biotas, the interpretation is less ambiguous. In the course of the ontogenesis, simultaneously with the process of elongation a process of apiculation takes place (/? increases). Studying the material of a biota of the Copper Age, I have succeeded in finding a correlation between R and N: R = 2(N-c) where c = 1.25. Summary — When collecting molluscs it is important to study the composition of the population. In addition to information on the biota, the particular phases of the species development can be cognized as well. The logarithmic spiral can be used in the analysis of discoid Planorbidae. In an interesting way, the growth of Anisus septemgyratus can be divided into two phases (Fig. 8), and the final number Fig. 11. Relationship between characteristic h and —. Curve of fully developed specimens (Szabadíj h kígyós). •— Fig. 12. Relationship between characteristic h and —. Curve of juvenile specimens (Szab badkígyós). Fig. 13. Mouth and teeth of Chondrula tridens. — Fig. 14. Percentage of different tooth variations occurring in the basic multitude and symbolical signs for the set of teeth. — Fig. 15. Formation of mouth of Chondrula tridens: a = sharp young mouth, b = rounding mouth, c = fully developed mouth with teeth