Millipedes also have multi-segmented bodies with a head and a long trunk made up of numerous body-rings, but unlike centipedes that have two pairs of legs attached to each segment, millipedes have a different structure. The first segment behind the head is known as the 'collum' from the Latin for neck or collar. It counts as the first body ring, but doesn't have any legs. The following three segments each bear a single pair, but the remaining segments from the fifth are effectively fused double or diplo-segments that each bear two pairs of legs. In some species the last segment may be legless. Similarly with some juveniles that are still developing. The term 'ring' is used when counting the segments, which starts with the 'collum', then the three individual segments, followed by the double segments. The final body part is known as the 'telson', which is made up of the preanal ring and a pair of valves to close off the end of the digestive system. Most species have either an elongated cylindrical or flattened body with more than twenty segments, each with an exoskeleton consisting of four chitinous plates; tergites above, pleurites on the side and sternites below where the legs attach. The two main exceptions are the tiny Polyxenus lagurus bristly species whose exoskeleton is soft and uncalcified, and the short-bodied pill millipedes described separately.

The head is typically rounded above and flattened below with mouthparts consisting of a pair of mandibles behind which is a plate known as the gnathochilarium, but lacking the forcipule 'poison claws' that the centipedes have. Millipedes have no need for these appendages as they are herbivores and detritus eaters, not predators. The antennae are relatively short and clubbed. Some species are blind, whilst others have simple eyes that may include a single ocellus or many that are grouped together in a patch to form an ocular field.

Young millipedes typically have only three pairs of legs, followed by up to four legless segments.  They continually moult as they grow, adding further legs and segments at each stage until they mature, although some species continue to moult even after they become adults. The process varies between species and orders.

The British List includes around 65 species, much the same as centipedes, but separated into eight rather than four orders. However, three of these orders can be immediately dismissed unless you're interested in non-native hothouse species. That leaves five important orders covering the millipedes that can be encountered naturally, as well as a fair number of non-native or rare and localised species. The first is POLYXENIDA in the basal subclass Penicillata, which is represented in Britain by a single species, then the four primary orders in the subclass Chilognatha; GLOMERIDA (pill millipedes), CHORDEUMATIDA (with no meaningful common name), POLYDESMIDA (flat-backed millipedes) and JULIDA (cylindrical or snake millipedes). I've identified just over twenty species that I may be able to find locally, some being easier than others! The following thumbnail photos link to further information and images for each order.

Whilst centipedes are reasonably well documented including an identification key, millipedes are poorly supported with only limited information. There are no books or guides, so all details have to be sourced from the internet, which is why some descriptions here are rather sparce. 

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