Two new millipede species of the genus Coxobolellus Pimvichai, Enghoff, Panha & Backeljau, 2020 (Diplopoda, Spirobolida, Pseudospirobolellidae)

Two new millipede species of the genus Coxobolellus Pimvichai, Enghoff, Panha & Backeljau, 2020 from Thailand are described: Coxobolellus saratani sp. nov. from Loei Province and Coxobolellus serratoligulatus sp. nov. from Uttaradit Province. The descriptions are based on gonopod morphology and two mitochondrial gene fragments (COI and 16S rRNA). The phylogenetic mtDNA analysis assigned the two new species unequivocally to the consistently well-supported Coxobolellus clade, in which they form a fifth subclade that was well supported by maximum likelihood analysis of 16S rRNA, though neither by Bayesian inference nor by COI. The two new Coxobolellus species share four conspicuous gonopodal synapomorphies of the genus: (1) the protruding process on the coxae of the 3rd (and sometimes 4th) pair of male legs, (2) a large, triangular coxae on the 4th–5th pair of legs, (3) a short process of the preanal ring protruding as far as, or slightly beyond, the anal valves, and (4) the posterior gonopod telopodite divided into two parts, with a conspicuous pore opening at the mesal margin at the end of the coxal part of the posterior gonopod. Thus, the two new species provide further evidence of the well-defined monophyly of the genus Coxobolellus. Finally, the paper provides an updated morphological identification key to all currently described Coxobolellus species.