Mitogenome and nuclear rRNA gene cluster of Austropeplea subaquatilis (Tate, 1880) from South Australia, with molecular and morphological comparison of A. cf. brazieri (Smith, 1882) from Victoria (Gastropoda, Hygrophila, Lymnaeidae)

Species of <i>Austropeplea</i> are lymnaeid snails endemic to Australia and New Zealand, and most are intermediate hosts of parasitic trematodes. Their taxonomy has long been uncertain due to the high phenotypic plasticity of most species. In this study, we used Oxford Nanopore sequencing technology to characterise the mitogenome and nuclear ribosomal RNA (rRNA) gene cluster of <i>Austropeplea subaquatilis</i> from South Australia to support comparative taxonomic investigations of this species. Then, <i>A. subaquatilis</i> was compared with A. cf. brazieri at both morphological and molecular levels. Morphologically, <i>A. subaquatilis</i> and A. cf. brazieri can be distinguished by shell morphometric indices, mantle edge morphology, pigmentation, and reproductive and neural anatomy. The two taxa differed by 1.9% in both the mitogenome and nuclear rRNA gene cluster. Sequence divergence was pronounced in the internal transcribed spacer (ITS) regions of the latter gene cluster, with nucleotide differences of 13.8% in ITS1 and 8.2% in ITS2. Phylogenetic analyses of sequence data for the mitochondrial <i>16S</i> gene and ITS2 placed the two taxa in distinct groups. Taken together, the integrative evidence presented herein supported species-level divergence between <i>A. subaquatilis</i> and A. cf. brazieri.