Characteristics
Millipedes range from 2 to 280 millimetres (0.079 to 11 in) in length, and can have as few as eleven, to over a hundred segments. They are generally black or brown in colour, although there are a few brightly coloured species.
The millipede's most obvious feature is its large number of legs. Having very many short legs makes millipedes rather slow, but they are powerful burrowers. With their legs and body length moving in a wavelike pattern, they easily force their way underground head first. They also seem to have some engineering ability, reinforcing the tunnel by rearranging the particles around it. Their bodies have segmented sections which makes them move in a wave-like form.
The head of a millipede is typically rounded above and flattened below and bears large mandibles. The body is flattened or cylindrical, with a single chitinous plate above, one at each side, and two or three on the underside. In many millipedes, these plates are fused to varying degrees, sometimes forming a single cylindrical ring. The plates are typically hard, being impregnated with calcium salts. Because they lack a waxy cuticle millipedes are susceptible to water loss, and must spend most of their time in moist or humid environments.
Unlike centipedes and other similar animals, each segment bears two pairs of legs, rather than just one. This is because each is actually formed by the fusion of two embryonic segments, and is therefore properly referred to as a "diplosegment", or double segment. The first few segments behind the head are not fused in this fashion, and the first segment is legless, called a collum segment while the second to fourth have one pair each. In some millipedes, the last few segments may also be legless. The final segment bears a telson.
Millipedes breathe through two pairs of spiracles on each diplosegment. Each opens into an internal pouch, and connects to a system of tracheae. The heart runs the entire length of the body, with an aorta stretching into the head. The excretory organs are two pairs of malpighian tubules, located near the mid-part of the gut.
The head contains a pair of sensory organs known as the Tömösváry organs. These are found just posterior and lateral to the antennae, and are shaped as small and oval rings at the base of the antennae. They are probably used to measure the humidity in the surroundings, and they may have some chemoreceptory abilities too. Millipede eyes consist of a number of simple flat lensed ocelli arranged in a group on the front/side of the head. Many species of millipedes, including cave-dwelling millipedes such as Causeyella, have secondarily lost their eyes.
According to Guinness World Records the African giant black millipede Archispirostreptus gigas can grow to 38.6 centimetres (15.2 in).
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