ALLOZYME HOMOZYGOSITY AND PHALLY POLYMORPHISM IN THE LAND SNAIL ZONITOIDES NITIDUS (GASTROPODA, PULMONATA)

Genetic variation in the pulmonate land snail Zonitoides nitidus was e xamined by means of allozyme electrophoresis in 17 European population s. We observed no heterozygotes, indicating that Z. nitidus consists o f several homozygous multilocus genotypes (strains) probably produced by self-fertilization. Nine strains were detected. Strains appeared no t to be equally distributed over the regions considered. One strain wa s strongly differentiated from the others, which is suggestive of a ta xonomic differentiation. Anatomically, two major phally types were dis tinguished: euphallics, with well-developed male reproductive organs, and hemiphallics, with weakly developed male reproductive organs. Both phally types were found together in natural populations, but euphally ratios were very low (0-19%; overall mean = 7.79%) and differed betwe en geographical regions (Belgium, Germany, and Sweden). In some popula tions, hemiphallic individuals were smaller compared to euphallic indi viduals although the difference is small and its biological significan ce remains to be established. We found no clear relation between phall y type and allozyme data.