Myriapoda
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Myriapoda is a subphylum of arthropods containing millipedes, centipedes and others. The group contains 13,000 species, all of which are terrestrial [2]. Although their name suggests they have myriad (10,000) legs, myriapods range from having over 750 legs (Illacme plenipes) [3] to having fewer than ten legs. They have a single pair of antennae and simple eyes.
Myriapods are most abundant in moist forests, where they fulfil an important role in breaking down decaying plant material [2], although a few live in grasslands, semi-arid habitats or even deserts [4]. The majority are herbivorous, with the exception of centipedes, which are chiefly nocturnal predators. Pauropodans and symphylans are small, sometimes microscopic animals that resemble centipedes superficially and live in soils. Millipedes differ from the other groups in having their body segments fused into pairs, giving the appearance that each segment bears two pairs of legs, while the other three groups have a single pair of legs on each body segment.
Although not generally considered dangerous to humans, many myriapods produce noxious secretions (often containing benzoquinones) which can cause temporary blistering and discolouration of the skin [5].
The fossil record of myriapods reaches back into the late Silurian, although molecular evidence suggests a diversification in the Cambrian Period [6], and Cambrian fossils exist which resemble myriapods [2].
[edit] Classification
There has been much debate as to which arthropod group is most closely related to the Myriapoda. Under the Mandibulata hypothesis, Myriapoda is the sister taxon to Pancrustacea, a group comprising the Crustacea and Hexapoda. Under the Atelocerata hypothesis, Hexapoda is the closest, whereas under the Paradoxopoda hypothesis, Chelicerata is the closest. This last hypothesis, although supported by few, if any, morphological characters, is supported by a number of molecular studies [7].
There are four classes of extant myriapods, Chilopoda (centipedes), Diplopoda, Pauropoda and Symphyla. While each of these groups of myriapods is believed to be monophyletic, relationships among them are less certain [8].
[edit] References
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- ^ Myriapoda (TSN 563885). Integrated Taxonomic Information System.
- ^ a b c Ben Waggoner (1996-02-21). Introduction to the Myriapoda. University of California, Berkeley.
- ^ Paul E. Marek & Jason E. Bond (2006-06-08). Biodiversity hotspots: rediscovery of the world's leggiest animal. Nature 441: 707. DOI:10.1038/441707a.
- ^ Myriapod. Britannica Concise Encyclopedia.
- ^ Strange and Unusual Millipedes.
- ^ Markus Friedrich & Diethard Tautz (2002). "Ribosomal DNA phylogeny of the major extant arthropod classes and the evolution of myriapods". Nature 376: 165–167. DOI:10.1038/376165a0.
- ^ Alexandre Hassanin (2006). "Phylogeny of Arthropoda inferred from mitochondrial sequences: strategies for limiting the misleading effects of multiple changes in pattern and rates of substitution". Molecular Phylogenetics and Evolution 38: 100–116. DOI:10.1016/j.ympev.2005.09.012.
- ^ Jerome C. Regiera, Heather M. Wilson & Jeffrey W. Shultz (2005). Phylogenetic analysis of Myriapoda using three nuclear protein-coding genes. Molecular Phylogenetics and Evolution 34: 147–158. DOI:10.1016/j.ympev.2004.09.005.
