The body is flattened or cylindrica

The body is flattened or cylindrical, composed of numerous metemeric segments, each with an exoskeleton consisting of 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.[8] Because they lack a waxy cuticle, millipedes are susceptible to water loss and must spend most of their time in moist or humid environments.[9]

The first segment behind the head is legless and known as a collum. The second to fourth body segments bear a single pair of legs each and are known as "haplosegments", from the Greek haplo, "single" (the three haplosegments are sometimes referred to as a "thorax"[10]). The remaining segments, from the fifth to the posterior, are properly known as diplosegments, or double segments. Each diplosegment bears two pairs of legs, rather than just one as in centipedes. This is because each diplosgment is formed by the fusion of two embryonic segments. In some millipedes the last few segments may be legless. The terms "segment" or "body ring" are often used interchangeably to refer to both haplo- and diplosegments. The final segment bears a telson, which consists of a legless preanal ring, pair of anal valves (closeable plates around the anus), and a scale below the anus.[6][8]

Millipedes in several orders have keel-like extensions of the body-wall known as paranota, which can vary widely in shape and size. Paranota may allow millipedes to wedge more securely into crevices, protect the legs, or make the millipede more difficult for predators to swallow.[11]


The head of a millipede is typically rounded above and flattened below and bears a pair of large mandibles in front of a plate-like structure called a gnathochilarium ("jaw lip").[6]

The head contains a single pair of antennae with seven or eight segments and a group of sensory cones at the tip.[6] Many orders also possess a pair of sensory organs known as the Tömösváry organs, shaped as small oval rings posterior and lateral to the base of the antennae. Their true function is unknown,[6] but they also occur in some centipedes, and are possibly used to measure humidity or light levels in the surrounding environment.[7]

Millipede eyes consist of a number of simple flat-lensed ocelli arranged in a group or patch on each side of the sides of the head. These patches are sometimes called ocular fields or ocellaria. Many species of millipedes, including the entire order Polydesmida and cave-dwelling millipedes such as Causeyella and Trichopetalum, have secondarily lost their eyes and are completely blind.[5]