The class Chilopoda includes five orders, 21 families, and 3,200 known species. Chilopoda belongs to the subphylum Myriapoda, which also includes millipedes (class Diplopoda) and two less diverse groups, the Pauropoda and Symphyla. The structure and function of the head endoskeleton and the mandible suggest that Myriapoda is a natural group, but some zoologists consider millipedes, pauropods, and symphylans to be more closely related to insects than to centipedes.
Four of the five living orders of centipedes share flattened heads and other adaptations for living in confined spaces, and the openings of the tracheal respiratory system are located above the legs on each side of the body. These features indicate that there is a more recent shared ancestry for the orders Lithobiomorpha (1,500 species), Craterostigmomophora (one or two species), Scolopendromorpha (550 species), and Geophilomorpha (1,100 species) than is shared with the order Scutigeromorpha (80 species). The latter group, also known as Notostigmophora, has a domed head, large multi-faceted eyes, and the openings of the tracheae are located on the upper side of the body at the back of each tergal plate. Scutigeromorphs have special tracheal lungs. It is only in the orders Scolopendromorpha and Geophilomorpha that hatch-lings emerge from the egg with their full adult number of segments. This so-called epimorphic development, the distinctive structure of the testes, and the tracheae having connections between the segments all indicate that these two orders are most closely related.
The earliest fossil centipedes are from the late Silurian (418 million years ago) of Britain, and belong to the order Scutigeromorpha. Other Paleozoic centipedes include the ex tinct order Devonobiomorpha (one species: Devonian, New York State), and late Carboniferous members of Scolopendromorpha and Scutigeromorpha. Fossils preserved in Tertiary amber are essentially modern.
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