Arthropod leg

This means that a greater number of segments is required to achieve the same kinds of movements that are possible in vertebrate animals, which have rotational ball-and-socket joints at the base of the fore and hind limbs.

The exopodites can sometimes be missing in some crustacean groups (amphipods and isopods), and they are completely absent in insects.

The claws of the scorpion are not truly legs, but are pedipalps, a different kind of appendage that is also found in spiders and is specialised for predation and mating.

The legs of crustaceans are divided primitively into seven segments, which do not follow the naming system used in the other groups.

The claw (chela) of a lobster or crab is formed by the articulation of the dactylus against an outgrowth of the propodus.

Myriapods (millipedes, centipedes and their relatives) have seven-segmented walking legs, comprising coxa, trochanter, prefemur, femur, tibia, tarsus, and a tarsal claw.

In most millipedes, one or two pairs of walking legs in adult males are modified into sperm-transferring structures called gonopods.

Prolegs do not have the same structure as modern adult insect legs, and there has been a great deal of debate as to whether they are homologous with them.

Some insects that exhibit hypermetamorphosis begin their metamorphosis as planidia, specialised, active, legged larvae, but they end their larval stage as legless maggots, for example the Acroceridae.

Among the Exopterygota, the legs of larvae tend to resemble those of the adults in general, except in adaptations to their respective modes of life.

Again, the young of the Coccoidea are called "crawlers" and they crawl around looking for a good place to feed, where they settle down and stay for life.

As a rule, the tibia of an insect is slender in comparison to the femur, but it generally is at least as long and often longer.

In the Apocrita, the tibia of the foreleg bears a large apical spur that fits over a semicircular gap in the first segment of the tarsus.

For example, the Pterogeniidae characteristically have 5-segmented fore- and mid-tarsi, but 4-segmented hind tarsi, whereas the Cerylonidae have four tarsomeres on each tarsus.

In the Neoptera, the parempodia are a symmetrical pair of structures arising from the outside (distal) surface of the unguitractor plate between the claws.

Webspinners (Embioptera) have an enlarged basal tarsomere on each of the front legs, containing the silk-producing glands.

[14] Under their pretarsi, members of the Diptera generally have paired lobes or pulvilli, meaning "little cushions".

The arolium, plantulae and pulvilli are adhesive organs enabling their possessors to climb smooth or steep surfaces.

Their structures are covered with tubular tenent hairs, the apices of which are moistened by a glandular secretion.

Tension on the long tendon is controlled by two muscles, one in the femur and one in the tibia, which can operate differently depending on how the leg is bent.

Tension on the long tendon controls the claw, but also bends the tarsus and likely affects its stiffness during walking.

[16] The typical thoracic leg of an adult insect is adapted for running (cursorial), rather than for digging, leaping, swimming, predation, or other similar activities.