MOLECULAR SYSTEMATICS OF THE FRESH-WATER SNAIL FAMILY LYMNAEIDAE (PULMONATA, BASOMMATOPHORA) UTILIZING MITOCHONDRIAL RIBOSOMAL DNA-SEQUENCES

Nucleotide sequences were obtained from a region of the large subunit mitochondrial ribosomal RNA gene from 18 lymnaeid taxa and a planorbid outgroup. A molecular phylogeny was constructed utilising maximum-par simony and distance analyses of the data. This agreed with certain asp ects of karyology and immunology-based lymnaeid taxonomy, but failed t o support the only previously published phylogenetic scheme or past in ferences regarding basal relationships in lymnaeids. The molecular phy logeny is also incongruent with previous progressive-evolution models based on chromosome numbers because European genera having n = 18 form ed a group basal within lymnaeids whereas taxa belonging to the n = 16 group included the most derived lymnaeids. Relationships of selected problematic taxa inferred from the molecular phylogeny were compared t o previous hypotheses based on other data sets. A partial, tentative b iogeographical hypothesis was derived from this phylogeny. We propose a Laurasian origin for lymnaeids in the late Jurassic.