Structural characteristics of mitochondrial genome of Spirobo-lus walkeri (Spirobolida: Spirobolidae), and phylogenetic analysis of Diplopoda

The phylogeny of Diplopoda, a group of ancient arthropod and an important component of modern terrestrial ecosystems, remains unclear. Here, the complete mitogenome of <i>Spirobolus walkeri</i> was determined. The newly sequenced complete mitogenome was circular DNA molecules with sizes of 14,879 bp. The mitogenome was composed of 37 genes and one control region. Negative AT-skews and positive GC-skews were found in whole mitogenome. The gene <i>COX1</i> used CGA as the start codon, while the other PCGs utilized ATN (A, T, G) as the start codons; however, the sequence of the stop codon was variable. The Ser2 exhibited the highest usage bias. All tRNAs have typical cloverleaf structures, except <i>trnS-AGC</i> and <i>trnM</i>. Phylogenetic analysis showed that <i>S. walkeri</i> and <i>Spirobolus bungii</i> shared a close relationship and that they were also closely related with <i>Narceus annularus</i>. This study helps resolve taxonomic ambiguities among morphologically similar species and provides data to support the establishment of evolutionary benchmarks for millipedes, including gene rearrangements and variations in tRNA structure.