Terrestrial pulmonate slugs are hermaphroditic and often are capable of both outcrossing and self-fertilization. This mixed breeding system may severely affect population genetic structuring and taxonomic differentiation. Currently little is known about the breeding system(s) of Banana slugs (Ariolimax), a group of taxonomically ill-defined slugs living along the West Coast of North America, from California to southern Alaska. Based on genital morphology and mtDNA sequence data (COI, 16S and CytB), the genus Ariolimax is nowadays interpreted as a group of eight species level taxa, viz Ariolimax columbianus, A. buttoni, A. stramineus, A. californicus, A. dolichophallus, A. brachyphallus and two undescribed species. These species ap-pear to be closely related as 19 microsatellite DNA loci identified from A. californicus consistently amplify in all of the de-scribed taxa and share many alleles. Hence, these microsatellites can help to clarify Ariolimax taxonomy. To this end, four microsatellite loci were used to study potential interspecific crosses of A. californicus x A. dolichophallus. This showed that none of these crosses produced hybrid offspring and that A. californicus reveals multiple paternity under natural conditions. Conversely, a panel of 28 microsatellites applied to cross-breeding experiment between two populations of A. buttoni, showed that all the parental specimens involved only three homozygous multilocus genotypes (MLG) and that offspring of pairs in which both parents had a different genotype, always were monomorphic for the same homozygous MLG of one of the parents. This confirms that A. buttoni is able to self-fertilize. Yet, to what extent self-fertilization is common in natural condi-tions remains to be investigated.

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