Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 71. (Budapest 1979)
Domokos, T.: On the morphological changes during ontogenesis of some Hungarian molluscs
On the Morphological Changes during Ontogenesis of Some Hungarian Molluscs by T. DOMOKOS, Békéscsaba Abstract — The increase of the whorls in the species of Planorbariuscorneus L. and Anisus septemgyratus ROSSM. is roughly exponential. The growth of P. corneus comprises one phase only, that of A. septemgyratus can be divided into a rapid and a slow period. In the species of Chondrula tridens O. F. MÜLLER the tooth variation of strong H 3 , G 3 and weak B is quite frequently found. There is almost a direct ratio between the shell elongation and height. In studying the changes of form of Unio shells the functionality established between the elongation and the length can be applied. With 17 figures. Introduction — Most malacologists do not collect juvenile specimens, or rather do not insist on the juvenile, living specimens or their empty shells found in leaf-litter or alluvium samples. In studying the dynamics of the population it is important to analyse the proportions of individual specimens in different states of development. The quantitative sequence of whichever parameter, although obtained from individual specimens of different age and in different states of development, gives valuable information on the situation of the species within the biota as well as on the species itself. In Figs. 1 and 2 some characteristic and informative linear diagrams are presented: 1. The high total percentage, the spread of the individual specimens growing old, rsp. perished in biota 1 show that the species lives in a favourable ecosystem, the shells are not carried away and they perish very slowly. — 2. The collection was of representative nature and did not cover living specimens, or no such were found in the examined area. The species perished, or it momentarily left the examined district. — 3. Our collection was made on a spot where the studied species is "conquering". The species migrated through a district where no other individual perished, or if it did, it had already been assimilated by the stratum. —• 4. We endeavoured to collect only dead specimens and from different biotas. Modus y is the most frequent value of single specimens living in a less favourable ecosystem. The diagram can be interpreted, of course, also as two populations following each other in time. The keeping of the shells decides in this case. — 5. The given number of samples is not sufficient for statistic studies. A right, reliable analysis demands very great circumspection and a time-consuming work. Repeated collections in the same biota should be performed. After measuring the living specimens must be returned to the ground. Without a good working knowledge of population dynamics, the analysis of the parameters cannot be completed. Studying population dynamics is also useful for when the characteristics of molluscs in different states of development are systematized, one can conceive the development trend of the species without having effectively followed the development of the given specimens. Studies of this type constitute the subject of this paper. (I omit the demonstration of the measuring methods and the expounding of the evaluation; thereof I have already spoken in my previous papers.) In my paper I study the development of the morphological characters of four species. Three of the four species are Gastropoda (as regards form, according to the nomenclature of MOSLEY 1838, two species are discoid and one is turbinai) and one is bivalve. In other words, I tried to choose species representing the molluscs living in Hungary. Results Discoid forms: Planorbarius corneus L. In studying the growth of the shell it is expedient to be performed in the plane perpendicular to the axis of the shell. The constants of the function describing a principally given logarithmic spiral should be determined.
