Diplopoda

(də′plä·pə·də)

(invertebrate zoology) The millipeds, a class of terrestrial tracheate, oviparous arthropods; each body segment except the first few bears two pairs of walking legs.

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A class of terrestrial, tracheate, oviparous arthropods. Diplopods (millipeds) are largely cryptic in habits, are saprophytic feeders, and are characterized by the development of a compact head with a pair of short, simple, eight-jointed antennae, and powerful mandibles. The body is not differentiated into thorax and abdomen, but is composed of a variable number of similar, cylindrical diplosomites, each of which (except the first two or three) bears two pairs of walking legs. The body wall is chitinous, with a thick impregnation of calcium carbonate in the majority of species. Most millipeds are variously adapted for rolling into a closed spiral or nearly perfect sphere when threatened.

The sexes are separate and fertilization is internal, following prolonged clasping behavior. Eggs may be laid in a cluster and “brooded” by the mother, scattered singly in the humus environment, or enclosed in an igloo-shaped mud nest built by the mother. Postembryonic development is gradual, without major changes in appearance, and may require a year or more for completion.

More than 8000 species have been described, although so far only the fauna of Europe is well known. In general, about 11 orders and more than 111 families are recognized. Probably as many as 25,000 species will eventually be recognized. Classification is based to a large extent upon shape of the male gonopods, which are quite constant and characteristic for each species.

Most species are local in distribution, because millipeds generally remain close to the parental habitat, and some may be restricted to a few square miles. Even genera are limited in distribution, and only a few occur on more than one continent.

The diplopods have a long geological history; they arose in the Early Devonian and were well developed by the Late Pennsylvanian. See also Arthropoda.

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IN BRIEF: n. - Arthropods having the body composed of numerous double somites each with two pairs of legs: millipedes.

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