The First Cavernicolous Species of Arrhopalites (Collembola, Symphypleona, Arrhopalitidae) from China and Its Phylogenetic Position

<i>Arrhopalites</i> Börner, 1906 includes 40 valid species, with 20 considered troglobionts, exclusive to caves. <i>Arrhopalites beijingensis</i> sp. nov. is the third species from China and the first from a cave habitat, collected in the Xianrendong Cave, Beijing, Junzhuang Town. It resembles several species of the <i>Caecus</i> group, possessing spine-like chaetae on the head, five to seven subsegments on Ant IV with annulated separations, and lacking cuticular spines on Abd VI; it differs from these species in its various characteristics. The mitogenome of <i>A. beijingensis</i> sp. nov. was assembled (14,774 bp in length), marking the first made available from the genus. Due to the incipient number of published mitochondrial genomes of Symphypleona, we downloaded raw sequencing data and performed the assemblies and annotations of 11 species. Our phylogenetic analyses comprised 24 mitogenomes in total; of those, 22 were of Symphypleona and 2 were of outgroups. <i>A. beijingensis</i> sp. nov. was placed closer to <i>Pygmarrhopalites spinosus</i> (Rusek, 1967), with high support. Arrhopalitidae was found as a sister group to Katiannidae, both part of Katiannoidea. The two species of Sminthuridida were placed as a sister group to all other Appendiciphora. More systematic analyses and enhanced sampling from key lineages are needed to better understand Symphypleona's internal relationships and evolution.