Pseudospirobolellidae is a poorly known family of spirobolidan millipedes with only two genera and five
described species. Yet, the descriptive taxonomy and molecular systematics of this group have been largely neglected.
Therefore, the present work presents an integrative taxonomic study of new pseudospirobolellid taxa in Thailand. To
this end, two mitochondrial gene fragments (COI and 16S rRNA) combined with morphological characters were used to
define the genus Coxobolellus, gen. nov. with 10 new species, viz. C. albiceps, sp. nov., C. compactogonus, sp. nov.,
C. fuscus, sp. nov., C. nodosus, sp. nov., C. serratus, sp. nov., C. simplex, sp. nov., C. tenebris, sp. nov., C. tigris, sp.
nov., C. transversalis, sp. nov. and C. valvatus, sp. nov. The interspecific COI sequence divergences among the new
species ranged from 6 to 15%. The intergeneric COI sequence divergence between species of Coxobolellus, gen. nov.,
Benoitolus birgitae and Pseudospirobolellus sp. ranged from 20 to 23%. Three major morphological differences
separate Coxobolellus, gen. nov. from Benoitolus and Pseudospirobolellus, namely (1) the protruding process on the 3rd
(and 4th) coxae on male legs, (2) the posterior gonopod telopodite divided into two parts, and (3) a conspicuous opening
pore at the mesal margin at the end of the coxal part of the posterior gonopod. Thus, the new genus is well supported by
both mtDNA and morphological evidence, while the delimitation of the 10 new species is supported by the congruence
between mtDNA and morphological data. Yet, with respect to the relationships of Benoitolus birgitae, morphological
data suggest a similarity with Coxobolellus, gen. nov. and Pseudospirobolellus, whereas mtDNA data place this species
in the Pachybolidae. Further phylogenetic analyses are needed to explore this apparent incongruence and test the
monophyly of Pseudospirobolellidae.