Sphaerobelum
Sphaerobelum is a genus of giant pill-millipedes in the family Zephroniidae, endemic to Southeast Asia, with most species occurring in Thailand, Laos and Vietnam. Members of this genus are characterised by volvation, jewel-like coloration and distinct morphological adaptations. Several species are restricted to limestone karsts and forested habitats and recent molecular studies confirm the genus' distinctness from closely related genera such as Zephronia.
Description
Sphaerobelum are medium to large-sized millipedes, capable of rolling into a tight ball when threatened which is a typical trait of the order Sphaerotheriida. Their bodies consist tergites, with a glossy exoskeleton that may exhibit colors such as turquoise and dark green depending on species. The also have ocelli and their antennae may be short and club-shaped. They have posterior telopods, with four podomeres and a large process on the second podomere with a large tip.
Sexual dimorphism is slightly evident in some species, particularly in the shape and size of the anal shields. The surface texture of the tergites ranges from smooth to hairy. The posterior margin of the collum are often diagnostic at the species level.
Additionally, male Sphaerobelums can be differentiated from other giant pill-millipede genera by the distally swollen process of the second joint of the posterior telopod.
Taxonomy
The genus was first described by Karl Wilhelm Verhoeff in 1924. Sphaerobelum belongs to family Zephroniidae, which includes species known for their ability to roll into tight spheres as a defense mechanism.
Recognised species
As of 2025, the genus includes at least 27 recognised species:Sphaerobelum aesculus Rosenmejer & Wesener, 2021Sphaerobelum benqii Liu & Wesener, 2022 Sphaerobelum bicorne Attems, 1938 Sphaerobelum bolavensis Wesener, 2019 Sphaerobelum cattiense Semenyuk, Golovatch & Wesener, 2018 Sphaerobelum clavigerum Verhoeff, 1924 Sphaerobelum denticulatum Wesener, 2019 Sphaerobelum hirsutum Verhoeff, 1924 Sphaerobelum huzhengkuni Zhao, Yu & W. Liu, 2020 Sphaerobelum konkakinhense Golovatch & Wesener, 2018 Sphaerobelum lachneeis Wesener, 2019 Sphaerobelum laoticum Wesener, 2019 Sphaerobelum meridionalis Bhansali & Wesener, 2022 Sphaerobelum nigrum Wesener, 2019 Sphaerobelum nonghinensis Srikampha & Srisonchai, 2025 Sphaerobelum onyx Srikampha & Srisonchai, 2025 Sphaerobelum peterjaegeri Wesener, 2019 Sphaerobelum petramurum Srikampha & Srisonchai, 2025 Sphaerobelum phouloei Wesener, 2019 Sphaerobelum pumatense Semenyuk, Golovatch & Wesener, 2020 Sphaerobelum schwendingeri Wesener, 2019 Sphaerobelum separatum Attems, 1953 Sphaerobelum spinatum Wesener, 2019 Sphaerobelum splendidum Wesener, 2019 Sphaerobelum truncatum Wongthamwanich, 2012 Sphaerobelum tujiaphilum Zhao & Liu, 2022 Sphaerobelum turcosa Srisonchai & Pimvichai, 2023
Ecology and behavior
Sphaerobelum are often associated with humid forest floors and limestone karsts. Many are endemic to single localities. For instance, Sphaerobelum truncatum is found in Nan Province, Northern Thailand, while Sphaerobelum turcosa is limited to Phu Pha Lom Forest Park in Loei Province.
Genetics
Molecular phylogenetic studies using mitochondrial COI gene sequences reveal significant genetic divergence between species of Sphaerobelum and other genera in Zephroniidae. The genus is genetically distinct from both Zephronia and other sphaerotheriid genera, with intergeneric distances reaching up to 32% in uncorrected p-distance.
Distribution
The genus is primarily distributed across Southeast Asia, especially in Thailand and Laos and Vietnam.