Myriapoda includes four
subclasses. Diplopoda (the millipedes) and Chilopoda (the centipedes) are names
familiar to most people. The two other subclasses, Pauropoda and Symphyla, comprise
more elusive creatures of dim, protected places such as leaf litter and dirt.
Myriapods are most noted for having many legs (ranging from <10 to a couple
hundred pairs) and there are some 13,000 extant species. Many species have glands
that secrete foul-tasting compounds as a chemical defense.
(centipedes) have one pair of legs per body segment, are predators, and the first
pair of are claws with poison glands that they use to capture prey.
(meaning double legs) include the millipedes. Each body segment is formed in early
development when two adjacent embryonic segments fuse, resulting in each adult
body segment having two pairs of legs. While some are carnivores, most feed on
are four groups of myriapods; how they are related to each other is not yet well
understood. Two of them, the Symphyla and Pauropoda, consist of tiny arthropods
living in leaf litter and soil; both superficially resemble centipedes. Symphylans
are lowly cousins of centipedes, and Pauropodans more closely resemble millipedes.
are eyeless, .5 to 8 mm, have 14 segments of which the first twelve have pairs
of legs. The Pauropods are also eyeless, are a tiny .5 to 1.5 mm, with only 9
to 11 segments, some of which are diplo-segments, like millipedes. Lack of site
renders these arthropods to a lowly existence.
Myriapods are relatively rare in the fossil record, a result of
a light and thin cuticle shell, and their existence in non-marine
environments where fossilization is less likely. The few older fossils,
however, are testament to the ancient appearance of these Arthropods.
The oldest fossil uniramians (single-jointed legs) are Myriapod-like
marine creatures from Cambrian-age strata. Fossil burrows in Ordovician
strata have led to conjecture that Myriapods might have been living
on land as early as 400 million years ago. However, some of the
first unequivocal terrestrial myriapods are recorded from rocks
of the Late Silurian and the oldest centipedes are from the Devonian.
millipedes are found in the famous Pennsylvanian-age
Mazon Creek site in Northern Illinois. Cenozoic examples are known
primarily from Oligocene amber. Mesozoic myriapod fossils are quite
rare. Myriapodous arthropods have been discovered in the Rhynie
chert where they appear to have formed a significant component of
the Early Devonian biota.
oldest myriapod in the fossil record, and possibly the oldest known
terrestrial oxygen-breathing organism is the millipede Pneumodesmus
newmani from the mid Silurian dating to about 425 million years
ago (Wilson and Anderson, 2004). It exhibits cuticular openings
that taxonomists have interpreted as spiracles, or atmospheric oxygen
intake organs. The oldest centipede in the fossil record is described
from macerates, or cuticle remnants from hydrofluoric acid-dissolved
rocks, of the Late Silurian, dating to about 415 million years ago
(Jeram, et al. 1990).
A. J., Selden, P. A. and Edwards, D. 1990. Land animals in the Silurian:
arachnids and myriapods from Shropshire, England. Science, 250,
H.M. and Anderson, L.I. 2004. Morphology and taxonomy of Paleozoic
millipedes (Diplopoda: Chilognatha: Archipolypoda) from Scotland.
Journal of Paleontology, 78(1):169-184.