A new genus of the millipede family Pseudospirobolellidae, Siliquobolellus gen. nov., is described from limestone mountains in Thailand, based on three new species, viz. Siliquobolellus amicusdraconis gen. et sp. nov. from Uthaithani Province, Siliquobolellus constrictus gen. et sp. nov. from Prachuap Khiri Khan Province and Siliquobolellus prasankokae gen. et sp. nov. (type species) from Lampang Province. The descriptions are based on gonopod morphology and mitochondrial DNA data (COI barcodes). The COI barcodes grouped the three new species in a well-supported Siliquobolellus gen. nov. clade. The mean interspecific COI sequence divergence among the three new species was 12% (range: 8–15%). The mean intergeneric COI sequence divergence between Siliquobolellus gen. nov., Coxobolellus Pimvichai, Enghoff, Panha & Backeljau, 2020, and Pseudospirobolellus Carl, 1912 was 19% (range: 14–23%). Three conspicuous gonopodal synapomorphies differentiate Siliquobolellus gen. nov. from other pseudospirobollellid genera: (1) the telopodital part of the posterior gonopod forms a deep concavity, (2) the telopodite of the anterior gonopod is directed distad and does not reach the tip of the coxal part of the anterior gonopod, and (3) the tip of the anterior gonopod coxa is narrowed, curving mesad. As such, the monophyly of the new genus is well supported by both morphological and mitochondrial DNA data. A distribution map and an identification key to the species are provided.

Key Words: COI, gonopod, monophyly, synapomorphy

Class Diplopoda de Blainville in Gervais, 1844

Order Spirobolida Bollman, 1893

Suborder Spirobolidea Bollman, 1893

Family Pseudospirobolellidae Brölemann, 1913

Etymology: From Latin siliqua = pod, and referring to the podlike shape of the gonopod telopodite. 

Diagnosis: Siliquobolellus species are characterised by (1) the unique shape of the telopodital part of their posterior gonopod, which forms a deep concavity. In contrast, the telopodital part of the posterior gonopod is extremely slender and sickle-shaped in Pseudospirobolellus, does not form a deep concavity in Coxobolellus, or is slender with a broad apical canopy in Benoitolus; (2) the telopodite of anterior gonopod (at) simple, directed distad, not reaching tip of coxal part of the anterior gonopod (cx). In contrast, the telopodite of anterior gonopod (at) is overreaching coxa in the other three genera; and (3) tip of anterior gonopod coxa narrowed, curving mesad. In contrast the tip of the anterior gonopod coxa directed distad in Coxobolellus, or is rounded in Pseudospirobolellus and Benoitolus.

Distribution: Known only from the type locality in Uthaithani Province, Thailand (Fig. 7).

Distribution: Known only from the type locality in Prachuap Khiri Khan Province, Thailand (Fig. 7).