Search

A regression model is proposed for studying the relationship between trace metals concentrations and weights of individuals of Monodonta turbinata (Born), a gastropod mollusc used as a trace metal biomonitor of marine coastal areas. The model herein presented was developed including sites as reference factors and showed very good correlations. The prevision model of contamination gave good results for this kind of pollutants, and it can be used as a tool for monitoring programmes.

Morphological and biochemical adaptations of two Mediterranean mollusks Gastrana fragilis and Monodonta turbinata to living in the littoral zone which is most exposed to abiotic factors are analyzed. Hemoglobin favoring to a certain extent their survival under constantly changing environmental conditions was quantified in the mollusks.

The effects of zinc and copper pollution on the allozymic variation of phosphoglucose isomerase (Pgi) genotypes were tested in the Mediterranean marine gastropods Monodonta turbinata and M. turbiformis in 26 laboratory tests involving 2 081 adult individuals, with 545 survivors. Our results indicate differential survivorship of electrophoretical Pgi allozyme genotypes for both pollutants. Zinc pollution selected against the allozyme genotype SS in M. turbinata, whereas no differential survivorship was observed in M. turbiformis which lacks this allozyme. Copper pollution selected against the MM genotype in both species. These results are inconsistent with the neutral theory of allozyme polymorphisms and appear to reflect the adaptive nature of some Pgi genotypes in these marine gastropods.

The sperm cells ofPatella coerulea (Patellacea),Monodonta turbinata, andGibbula tumida (Trochacea) were investigated by means of transmission electron microscopy. They belong to the primitive type (sensu Franzen) and have more features in common with primitive Bivalvia sperms than with Neritacea. Their head contains an apical acrosome and a roundish nucleus followed by 4 or 5 mitochondria and a centriolar apparatus which consists of two centrioles, one of which bears a flagellum. The sperm cells ofMonodonta andGibbula are very similar to each other and differ mainly in size;Patella exhibits more differences (very small acrosome, subacrosomal space, variable number of spherical mitochondria (origin of spermic dimorphism ?). The development of the sperm cells shows no peculiarities.

THE trochids Monodonta turbinata and Gibbula divaricata are midlittoral and sublittoral animals respectively. On the rocky shores of Malta, M. turbinata is found semi-exposed in the very narrow “intertidal” zone. G. divaricata is usually found submerged in shallow water. It was considered that G. divaricata might be adapted for prolonged submersion by having among other factors a higher capacity to incur an oxygen debt than M. turbinata. The experiments described here were carried out to test this hypothesis.