POLYDESMIDA MILLIPEDE |
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Introduction to the Identification of Insects and Related Arthropods (PDF)
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KINGDOM : Animalia
PHYLUM : Arthropoda
SUBPHYLUM : Myriapoda
CLASS : Diplopoda
SUPERORDER : Merocheta
ORDER : Polydesmida
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POLYDESMIDA MILLIPEDE Flatback millipedes
Polydesmidans have between 19 and 20 segments and are cylindrical but many species have wing-like lateral extensions to the tergites called paranota, giving the group its common name of flat-backed millipedes. The dorsal plates and paranota are often ornamented with ridges, tubercles, and patches of colour. All polydesmidans lack eyes, and the great majority of species have either 58 or 62 legs as adults with one leg pair on each of the first three leg-bearing segments, and two leg pairs on each of the posterior 13 or 14 leg-bearing segments. The eighth leg pair in mature males is replaced by structures called gonopods, used to transfer sperm during mating. Gonopod variations are of great importance in polydesmidan taxonomy and are often the only practical basis on which to distinguish species. They have many pores along their body that produce hydrocyanide, formic acid and other irritants used for defense. Most species release the liquid slowly, but some can discharge it as a spray.
Polydesmida is by far the largest order of millipedes, with over 5000 species described worldwide. Polydesmida occur almost everywhere except Antarctica and the high Arctic. They are particularly diverse in tropical forests, but even in the temperate zone it is not unusual for a single patch of forest or grassy woodland to be home to 5-10 species of Polydesmida.
Polydesmida are poor dispersers under natural conditions and seem to be very good at evolving new species. As a result, many polydesmidan species have small geographical ranges (100-1000 square kilometres). Some Polydesmida are only known to occur at a single locality, such as a particular mountain. Polydesmidan genera are also good at forming distribution mosaics, in which each species occupies its own patch on the map and overlaps very little with other species in the same genus.
Male polydesmids mate by wrapping themselves around the female and transferring a spermatophore from their gonopore to the female gonopore with the use of specially modified legs. These legs or gonopods are always on body segment 7, which is the third segment carrying two pairs of legs. Eggs are laid in cavities or chambers in the soil and guarded by the female until hatching. The juveniles possess only three pair of legs and seven body segments. Subsequent moults increases both the number of segments and legs until the adult number is reached.
Polydesmid millipedes feed on decaying vegetation or a variety of live plants, including the leaves and shoots of ornamental plants and cultivated vegetables.
Polydesmid millipedes are common in all environments, dwelling in leaf litter, under rocks, and under the bark of rotting logs and living trees.
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