Mitochondrial genomes of Meghimatium pictum and Succinea arundinetorum provide insight into the gene order rearrangement within Stylommatophora (Gastropoda, Panpulmonata)

In this study, we report the whole mitochondrial genomes of two species, Meghimatium pictum and Succinea arundinetorum , which belong to Stylommatophora, one of the most abundant orders of Gastropoda. The total sizes of M. pictum and S. arundinetorum mitogenomes are 14,352 bp and 15,282 bp, with surprisingly biased proportions of A + T contents that reach to 72.1% and 76.78%, respectively. The protein coding genes (PCGs) in two mitogenomes show negative AT skew values and evolved primarily under purifying selection. Compared with the ancestor of stylommatophora, the mitochondrial genes of M. pictum exhibited multiple rearrangement events while the mitochondrial genes of S. arundinetorum showed only minor differences. Moreover, the order of PCGs were conserved while the tRNA genes showed high frequency of rearrangement among the stylommatophoran species, suggesting that the latter could be one of the major driving forces of mitogenomic evolution in terrestrial molluska species. Our research lays a theoretical foundation for investigating the evolution and divergence of mitochondrial genes and provides valuable resources for studying evolutionary genetics in stylommatophoran species.