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.