Chordeumatida

Chordeumatida can be distinguished from other millipede orders by several key features: the presence of six large dorsal setae per segment (three per side), a narrow collum creating a 'necked' appearance, a longitudinal dorsal groove, and the absence of ozopores. The combination of teloanamorphic development and spinnerets on the telson is unique to this order within the superorder Nematophora. Species with paranota can be distinguished from the superficially similar Polydesmida by the presence of the dorsal groove. The specific number of body segments (26–32) and leg pairs varies among species and can aid in identification. Male gonopod morphology, particularly which leg pairs are modified (pairs 7–11 in various combinations depending on family), provides critical diagnostic characters for family- and genus-level classification.

Chordeumatidans display highly variable body forms, including cylindrical and flat-backed morphologies. Most species possess 26 to 32 body segments behind the head (including the telson), with the number typically fixed within species. Body length ranges from 3.5 mm to 42 mm, though most species measure 10–25 mm. Coloration is generally drab, ranging from various shades of brown to unpigmented, though some species exhibit distinct patterns. A diagnostic feature is the presence of six large setae (bristles) on the dorsal surface of each body segment, three per side. The first segment (collum) is relatively narrow, creating a distinct 'neck' appearance in many species. The body tapers posteriorly and features a longitudinal dorsal groove. Some species possess paranota—lateral exoskeletal extensions—though these are absent in many. Unlike most helminthomorph millipedes, chordeumatidans lack ozopores (defensive gland openings). Adult females typically have 50 leg pairs, while adult males have 48 walking leg pairs plus two pairs modified as gonopods (pairs 8 and 9), though extensive variation exists across families.

Chordeumatidans occupy diverse habitats across their broad geographic range. Many species inhabit cold, rocky, mountainous areas, particularly in Europe and central Asia. The order includes troglobiotic (cave-dwelling) species, such as those in the genera Zygonopus and Scoterpes, as well as troglophilic species that occur in cave entrances and similar dark, humid microhabitats. Surface-dwelling species are found in forest litter, soil, and rocky debris. Some species show stenoendemic distributions restricted to small areas, such as specific cave systems or mountain valleys.

Chordeumatida occurs on all continents except Antarctica, representing a nearly worldwide distribution. The order is present in the tropics of Central America, Southeast Asia, and Oceania, extending south to Tasmania, New Zealand, and Chiloé Island, Chile. Species occur in Madagascar but are absent from sub-Saharan Africa and largely absent from South America outside of southern Chile. In the Northern Hemisphere, they range north to Scandinavia, Siberia, Canada, and southwest Alaska. The Caucasus region represents a major biodiversity hotspot for the order, particularly for the family Anthroleucosomatidae. Northwestern North America serves as the center of diversity for the family Conotylidae.

Chordeumatidans develop through teloanamorphosis, a mode of post-embryonic development in which individuals add segments and legs through successive molts until reaching a species-specific fixed number in the adult stage, after which molting ceases entirely. This distinguishes the order from most other millipede orders, which continue molting as adults (euanamorphosis or hemianamorphosis). In typical species, development proceeds through nine stages: hatchlings emerge with 6 segments and 3 leg pairs, progressing through stages with 8, 11, 15, 19, 23, 25, and 28 segments before reaching adulthood with 30 segments. Males typically begin gonopod development in the seventh stage. Species with non-standard adult segment numbers deviate from this pattern accordingly. Adult females use silk-producing spinnerets on the telson to construct protective chambers for molting and egg-laying.

A defining behavioral trait of Chordeumatida is the use of silk produced by spinnerets on the telson to construct protective chambers. These silk nests serve as shelters for molting and as egg-laying sites. The production of silk for nest-building is unique to this order within millipedes and has earned members the common name 'spinning millipedes.' Some species in the family Trichopetalidae produce a sticky secretion from the bases of segmental setae, possibly serving a defensive function.

Chordeumatidans function as decomposers in forest floor and soil ecosystems, contributing to nutrient cycling through consumption of decaying organic matter. Cave-dwelling species occupy detritivore niches in subterranean food webs, processing organic material entering cave systems. Some species serve as prey for cave-adapted predators; for example, the cave orbweaver spider Meta ovalis has been documented preying on the chordeumatidan millipede Causeyella (family Trichopetalidae).

Chordeumatidans have limited direct human relevance. They are not agricultural pests and pose no threat to human health. The order has received scientific attention due to its diverse developmental modes, unique silk-producing capabilities, and high diversity in biodiversity hotspots such as the Caucasus. Cave-dwelling species contribute to the recognized conservation value of subterranean ecosystems. Some species have restricted distributions, making them subjects of biogeographic and conservation interest.

• PolydesmidaSome Chordeumatida possess paranota similar to those in Polydesmida, but can be distinguished by the presence of a dorsal groove and six large setae per segment in Chordeumatida, versus the absence of these features in Polydesmida.
• JulidaBoth orders are abundant in European habitats and share general helminthomorph body plans, but Julida exhibits euanamorphosis (continued molting and segment addition in adults) rather than teloanamorphosis, and lacks the distinctive six-setae dorsal pattern and silk-producing spinnerets of Chordeumatida.
• Other NematophoraWithin the superorder Nematophora, Chordeumatida is distinguished by the combination of teloanamorphosis and silk-producing spinnerets; other orders in this superorder (Callipodida, Stemmiulida) lack these features or exhibit different body plans.

• millipede
• diplopoda
• teloanamorphosis
• silk production
• cave-dwelling
• decomposer
• mountain fauna
• European fauna
• North American fauna
• troglobiont
• troglophile

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Bug Eric: Spider Sunday: Cave Orbweaver
• Revision of the family Heterolatzeliidae (Diplopoda, Chordeumatida)
• Atlas of European millipedes 3: Order Chordeumatida (Class Diplopoda)
• The milliped genus Underwoodia (Chordeumatida: Caseyidae)
• The millipede order Chordeumatida (Diplopoda) in Kazakhstan, with descriptions of three new species
• Mecogonopodium carpathicum n. sp. (Diplopoda: Chordeumatida: Attemsiidae), a new troglophilic millipede from Slovakia
• A new species of the family Heterolatzeliidae from the Balkan Peninsula (Diplopoda, Chordeumatida)
• The milliped family Trichopetalidae, Part 2: The genera Trichopetalum, Zygonopus and Scoterpes (Diplopoda: Chordeumatida, Cleidogonoidea)
• The Caucasus as a major hotspot of biodiversity: Evidence from the millipede family Anthroleucosomatidae (Diplopoda, Chordeumatida)
• Tingupa tlingitorum, n. sp., a new milliped from Haines, Alaska, USA, with notes on the generic distribution and a revised key to species (Chordeumatida: Tingupidae)
• The millipede family Diplomaragnidae in Taiwan, with descriptions of nine new species (Diplopoda, Chordeumatida)
• Cave millipeds of the United States.  V. The genus Idagona Buckett & Gardner (Chordeumatida, Conotylidae, Idagoninae)
• Melogona sintica sp. nov.—a surprising seventh member of Melogona Cook, 1895, with a key to species of the genus (Diplopoda: Chordeumatida: Chordeumatidae)
• The millipede family Conotylidae in northwestern North America, with a complete bibliography of the family (Diplopoda, Chordeumatida, Heterochordeumatidea, Conotyloidea)