Nannaria

Difficult to identify to species without examination of male gonopods under magnification. The two species groups are distinguished by gonopod morphology: minor group has simple, stick-like gonopods, while wilsoni group has complex, twisting gonopods. Geographic distribution provides additional clues: wilsoni group is restricted to the Appalachian Mountains, while minor group occurs throughout eastern North America. The genus is distinguished from other Xystodesmidae by its cryptic (non-aposematic) coloration and subterranean habits. Unlike colorful Appalachian xystodesmids that form Müllerian mimicry rings, Nannaria lacks bright warning coloration.

Small-bodied millipedes measuring 15–38 mm in length. Coloration is cryptic: typically chestnut brown to black, often with orange, red, or white spots; uncommonly striped. Olive to black individuals may display pink keels or paranota. Lacks the bright aposematic coloration of other Xystodesmidae. Diagnostic morphological features include laterally positioned repugnatorial pores, paired gonopod processes, spatulate twisted pregonopodal claws (the source of the common name), and subcoxal sternal spines. Gonopods are sexually dimorphic and species-diagnostic: minor group has simple stick-like gonopods, while wilsoni group has complex twisting gonopods.

Mesic microhabitats in deciduous forests, particularly in middle to high elevation areas for the wilsoni group. Found in leaf litter and upper soil layers, typically 2–3 cm beneath the surface. Collected by removing leaf litter, turning rocks and logs, or via pitfall traps. Suitable habitat occurs in forested areas with accumulated organic matter. The wilsoni group shows affinity for middle to high elevation forests in the Appalachians, while the minor group occupies broader forested habitats across eastern North America.

Eastern United States. The minor species group: from western Arkansas and Missouri to just outside Rochester, New York in the north, and from the coast of Virginia to central Mississippi in the south. The wilsoni species group: restricted to the Appalachian Mountains, with a notable distribution gap in northeastern Tennessee and adjacent northwestern North Carolina that separates northern and southern portions of its range. New species are expected to be discovered in the southern Appalachian Mountains.

Decaying leaves and other plant matter.

Juveniles require maturation before definitive identification is possible; in laboratory settings, juveniles have been housed in terraria until maturation.

Strongly subterranean and cryptic. Adults tend to remain buried in soil, either completely beneath the surface or with only a portion of the body exposed. Does not exhibit extensive diurnal surface-level activity compared to other xystodesmids. This behavior makes deliberate collection difficult through traditional surface-searching methods. When disturbed, can release defensive chemicals from laterally positioned repugnatorial pores.

Decomposer in leaf litter and soil habitats. Breaks down decaying plant material, releasing nutrients into the ecosystem.

Subject of recent taxonomic research that brought public attention to millipede diversity, including the species Nannaria swiftae named after singer-songwriter Taylor Swift in 2022. The genus serves as an example of cryptic, understudied invertebrate diversity in eastern North American forests. Many species have small geographic ranges and may warrant conservation attention.

• Other XystodesmidaeNannaria lacks the bright aposematic coloration (red, yellow, black patterns) that characterizes many Appalachian xystodesmids such as Apheloria and Brachoria, which form Müllerian mimicry rings. Nannaria is also more subterranean and less surface-active than these colorful relatives.
• Oenomaea pulchellaSister taxon to Nannaria within tribe Nannariini; distinguished by morphological and molecular characters. Nannaria is more species-rich and geographically widespread.

• millipede
• diplopoda
• polydesmida
• xystodesmidae
• appalachian
• cryptic
• subterranean
• decomposer
• leaf litter
• soil fauna

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Top new species discoveries for the first half of 2022
• A revision of the minor species group in the millipede genus Nannaria Chamberlin, 1918 (Diplopoda, Polydesmida, Xystodesmidae)
• A revision of the wilsoni species group in the millipede genus Nannaria Chamberlin, 1918 (Diplopoda, Polydesmida, Xystodesmidae)