Not to be confused with Platydesmida or Polyzoniida.
Polydesmida (from the Greek poly "many" and desmos "bond") is the largest order of millipedes, containing approximately 3,500 species, including all the millipedes reported to produce hydrogen cyanide (HCN).

Description

Members of the order Polydesmida are also known as "flat-backed millipedes", because on most species, each body segment has wide lateral keels known as paranota. These keels are produced by the posterior half (metazonite) of each body ring behind the collum. Polydesmids have no eyes, and vary in length from 3 to 130 mm (0.12 to 5.12 in). Including the telson, adults have 19 or 20 rings, while juveniles may have from 7 to 19 rings. Mature males have a single pair of gonopods consisting of the modified forward leg pair of the 7th segment. Many of the larger species show bright coloration patterns which warn predators of their toxic secretions.

Ecology

Polydesmids are very common in leaf litter, where they burrow by levering with the anterior end of the body.

Classification

The c. 3500 species of Polydesmida are variously classified into four suborders (names ending in "-idea"), and 28 families, the largest (numerically) including Paradoxosomatidae, Xystodesmidae, and Chelodesmidae.

Dalodesmidea Hoffman, 1980. 2 families
Dalodesmidae Cook, 1896
Vaalogonopodidae Verhoeff, 1940
Leptodesmidea Brölemann, 1916. 13 families
Chelodesmoidea Cook, 1895
Chelodesmidae Cook, 1895
Platyrhacoidea Pocock, 1895
Aphelidesmidae Brölemann, 1916
Platyrhacidae Pocock, 1895
Rhachodesmoidea Carl, 1903
Rhachodesmidae Carl, 1903
Tridontomidae Loomis & Hoffman, 1962
Sphaeriodesmoidea Humbert & de Saussure, 1869
Campodesmidae Cook, 1896
Holistophallidae Silvestri, 1909
Sphaeriodesmidae Humbert & de Saussure, 1869
Xystodesmoidea Cook, 1895
Eurymerodesmidae Causey, 1951
Euryuridae Pocock, 1909
Gomphodesmidae Cook, 1896
Oxydesmidae Cook, 1895
Xystodesmidae Cook, 1895
Paradoxosomatidea Daday, 1889.[a] 1 family
Paradoxosomatidae Daday, 1889
Polydesmidea Pocock, 1887. 12 families
Oniscodesmoidea Simonsen, 1990
Dorsoporidae Loomis, 1958
Oniscodesmidae DeSaussure, 1860
Pyrgodesmoidea Silvestri, 1896
Ammodesmidae Cook, 1896
Cyrtodesmidae Cook, 1896
Pyrgodesmidae Silvestri, 1896
Haplodesmoidea Cook, 1895
Haplodesmidae Cook, 1895
Opisotretoidea Hoffman, 1980
Opisotretidae Hoffman, 1980
Polydesmoidea Leach, 1815
Cryptodesmidae Karsch, 1880
Polydesmidae Leach, 1815
Trichopolydesmoidea Verhoeff, 1910
Fuhrmannodesmidae Brölemann, 1916
Macrosternodesmidae Brölemann, 1916
Nearctodesmidae Chamberlin & Hoffman, 1958
Trichopolydesmidae Verhoeff, 1910
Representative diversity of Polydesmida

Asiomorpha coarctata (Paradoxosomatidae), an Asian species widely introduced by humans

Tasmaniosoma armatum (Dalodesmidae) from Tasmania

Eutrichodesmus aster (Haplodesmidae) from Vietnam, with unusual mid-dorsal crests

A species of Xystodesmidae from the United States showing aposematic coloration

An paradoxosomatid from China, with reduced paranota

Polydesmus collaris (Polydesmidae) from Europe



source - Wikipedia