Myriapods are terrestrial arthropods with many legs. Centipedes, millipedes and the lesser known pauropods and symphylans are the four main groups of myriapods. None of them have a thousand legs, as the name millipede suggests. The maximum count is 175 pairs, which is still a lot of legs!
The centipedes (Class Chilopoda) are predatory and they use their formidable mandibles to bite, tear and chew. They are also equipped with a set of poison claws, a modified set of hollow legs on the seventh segment with poison glands attached. The first six segments make up the head, equipped with mouth and jaws, a single pair of antennae and small or no eyes. The head is followed by a variable number of body segments, each with a pair of legs and a pair of respiratory spiracles. The body is usually flattened and the tail end has a pair of legs modified into feelers.
Because of their predatory nature, centipedes are fast and potentially dangerous. Their bite is painful and in at least one case, fatal. They are found in leaf litter and lurking under rocks, bark and fallen wood. They do not like light and rest during the day, coming out at night to hunt and feed. Some species live in caves and still others are burrowers and never come above ground. Female centipedes lay clusters of eggs and then may curl around and brood them until they hatch. Young centipedes are small versions of the adults and like all Arthropods, they must shed their outer cuticle in order to grow.
Millipedes (Class Diplopoda) are just the opposite in character to centipedes, being slow and quiet herbivores. They tend to be rounded instead of flattened and have two pairs of legs and two pairs of spiracles on each segment. This is a secondary characteristic that occurs during larval development when each pair of body segments fuse into one but keeping both two pairs of legs and spiracles. They have eyes that superficially resemble the compound eyes of insects but on closer inspection are just clusters of simple eyes.
Millipedes are important members of soil communities, consuming mosses, fungi, leaves and other decomposing plant materials. Although they have twice as many legs, they move much slower than centipedes, but then they do not have to catch their food. Their main forms of defence are to roll up into a ball and secrete noxious chemicals to fend off potential predators. They also lead secretive lives under rocks and wood and in the leaf litter during the day and coming out at night to feed.
The third group of myriapods is the Class Pauropoda, with about a hundred species of blind, soft-bodied soil dwellers. They are usually quite small, only a half to two mm long. They have conical heads with branched antennae and deep-set mandibles. There are no eyes but instead they have sense organs called pseudoculi which probably just sense light without forming images. The head is separated from the rest of the body by a ring and the trunk has 11 segments with legs on the first nine. There is no heart, circulatory system or respiratory organs. Sexes are separate and fertilisation is internal. The juvenile hatches with only three pairs of legs. Pauropods appear to be intermediate between millipedes and centipedes. They have single pairs of legs on each segment like centipedes but show some fusion of segments near the back in, as in the millipedes.
The fourth group of myriapods is the Class Symphyla. This is a widespread but small group of centipede-like animals with twelve pairs of legs and silk-spinning spinnerets on the thirteenth body segment. They are small, blind and white and can move very quickly. They eat both live and decaying plant material. Symphylans have maxillae that resemble those in insects and have other primitive insect characteristics as well, which makes them interesting from an evolutionary point of view, as they may be survivors of the original insect line. At least one species, the glasshouse symphylan, is a common garden pest in North America where it attacks the root hairs of crop species.
While writing this article, I remembered a childhood riddle. The answer is after the references. What goes 99 thump, 99 thump?
References: Buchsbaum, R. 1968. Animals without Backbones. Penguin Press Ed. Lindsey and Morris 2007. Field Guide to New Zealand Wildlife. Harper Collins Meglitsch, P. 1972. Invertebrate Zoology. Oxford University Press http://mint.ippc.orst.edu/symphid.htm http://www.kendall-bioresearch.co.uk/myriapod.htm
a centipede with a wooden leg
