Background: Semicerura bryophila Potapov & Sun, 2020 is a soil-dwelling springtail belonging to the family Isotomidae. The phylogenetic relationships among species of this group remain controversial due to a lack of molecular data. Therefore, in this study, we sequenced the mitochondrial genome of S. bryophila, analyzed the characterization of the mitochondrial genome, and investigated the phylogenetic relationships of Isotomidae. Methods: The mitochondrial genome of S. bryophila was sequenced and assembled. We analyzed the sequence length, nucleotide composition, and evolutionary relationships within the Isotomidae family, incorporating data from twelve previously published mitochondrial genomes. Results: The length of the S. bryophila mitogenome is 15,247 bp and comprises 13 protein-coding genes, 22 tRNAs, and two rRNAs, arranged in a typical order. Its base composition is as follows: A = 38.05%, T = 33.64%, G = 10.17%, and C = 15.03%. Phylogenetic analysis based on the mitogenome revealed that the monophyly of Isotomidae and the paraphyletic grouping of Semicerura and Folsomotoma, supporting their closer relationship with the subfamily Anurophorinae rather than to Isotominae. The analysis validated subfamily Anurophorinae, identified Pachyotominae as a part of Anurophorinae, and suggested that Isotominae is paraphyletic. Conclusions: The present study provides valuable mitochondrial information for the classification of S. bryophila and offers new insights into the taxonomic and evolutionary studies within the genus Semicerura.

Primary forests harbor extraordinary biodiversity, but conversion from primary forests to secondary forests often leads to biodiversity loss and diminished ecosystem functioning. While much of the existing research has focused on plants and vertebrates, soil fauna—particularly Collembola—remain underexplored in this context. To address this gap, we conducted a comprehensive assessment of the Collembola diversity and community composition in primary and secondary forests across two regions in northeastern China. Among 5587 Collembola individuals, 69 morphospecies were identified. The Collembola abundance and Shannon–Wiener index were significantly higher in primary forests, although the species richness did not differ significantly between the forest types. In contrast, the community composition differed markedly, with several taxa found exclusively in primary forests. Notably, environmental factors exerted stronger influences on Collembola communities in primary forests, suggesting that these ecosystems may be more vulnerable to climate change and external disturbances. These findings demonstrate that primary forests play a crucial role in protecting soil fauna diversity and emphasize that future conservation efforts should focus on the strict protection of primary forests.