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RESEARCH PRODUCT

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The living freshwater gastropod Melanopsis dufouri (FERUSSAC) has two morphotypes. The study of chemical variation of trace-elements in this gastropod and its correlation with the environmental fluctuation are the aim of this paper. Due to the genus Melanopsis has an abundant fossil record during the Cenozoic, the results of the present work could be of paleoecological interest. Trace-elements are embodied in the shell during growth. The shell of M. dufouri has accretionary growth. There are several examples cited on circadian accretionary growth in invertebrate shells. However, in the present case and as a first conclusion, the accretion rate depends on the size of the shell. In a short-time field study (l month) that has been carried out we are found some shells with circadian accretion. Chemical compositions of growth lines are generelly not related to dialy fluctuations of environmental parameters. There are gastropods of this species more sensitive to these parameter:> than others. This fact could be due to genetic variability. In a long-time field study (7 months) also carried out, the most significant environmental variation observed concerns to temperature in this period. The chemical composition of one of the two morphotypes is very sensitive to variations of environmental parameters. The other morphotype does not seem to be enough sensitive to environmental variation. The possible circadian accretion rates in M. dufouri does not agree with many general results about accretionary growth of invertebrate shells. It should be interesting analizing the reported cases of Circadian rates in shells under the assumptions of too paper. Paleoecological applications of our results are very difficult for fossil species of Melanopsis .