Arthropod leg

Arthropod Leg

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Arthropod leg

The arthropod leg is a form of jointed appendage

Appendage

Arthropod

Arthropods are animals belonging to the Scientific classification Arthropoda , and include the insects, arachnids, crustaceans, and others....
s, usually used for walking

Walking

Walking is the main form of animal locomotion on Earth, distinguished from running and crawling . When carried out in shallow waters, it is usually described as wading and when performed over a steeply rising object or an obstacle it becomes scrambling or climbing....
. Many of the terms used for arthropod leg segments are of Latin

Latin

Latin is an Italic language, historically spoken in Latium and Ancient Rome. Through the Military history of the Roman Empire, Latin spread throughout the Mediterranean and a large part of Europe....
origin, and may be confused with terms for bones: coxa (meaning hip

Hip (anatomy)

In anatomy, the hip or coxa in medical termonology is the bone projection of the femur which is known as the greater trochanter, and the overlying muscle and fat....
), trochanter (compare greater trochanter

Greater trochanter

The greater trochanter of the femur is a large, irregular, quadrilateral eminence.It is directed a little lateralward and backward, and, in the adult, is about 1 cm....
and lesser trochanter

Lesser trochanter

The lesser trochanter of the femur is a conical eminence, which varies in size in different subjectsIt projects from the lower and back part of the base of the Femur neck....
), femur
Femur

The femur, or thigh bone, is the most proximal bone of the leg in vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs....
, tibia
Tibia

The tibia, shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates and connects the knee with the ankle bones....
, tarsus
Tarsus (skeleton)

In tetrapods, the tarsus are the cluster of bones in the foot between the tibia and fibula and the metatarsus. The bones of the tarsus do not belong to individual toes, whereas those of the metatarsus do....
, ischium, metatarsus
Metatarsus

The metatarsus consists of the five long bones of the foot, which are numbered from the Anatomical terms of location side ; each presents for examination a body and two extremities....
, carpus
Carpus

In tetrapods, the carpals is the sole cluster of the bones in the wrist between the radius and ulna and the metacarpus. The bones of the carpus do not belong to individual fingers , whereas those of the metacarpus do....
, dactylus (meaning finger

Finger

A finger is a type of digit , an organ of manipulation and sensation found in the hands of humans and other primates.Normally humans have five digits, termed phalanges, on each hand ....
), patella
Patella

The patella, also known as the knee cap or kneepan, is a thick, triangular bone which articulates with the femur and covers and protects the knee joint....
.

Homologies of leg segments between groups are difficult to prove and are the source of much argument.

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Encyclopedia

The arthropod leg is a form of jointed appendage

Appendage

Arthropod

Arthropods are animals belonging to the Scientific classification Arthropoda , and include the insects, arachnids, crustaceans, and others....
s, usually used for walking

Walking

Latin

Hip (anatomy)

Greater trochanter

The greater trochanter of the femur is a large, irregular, quadrilateral eminence.It is directed a little lateralward and backward, and, in the adult, is about 1 cm....
and lesser trochanter

Lesser trochanter

Finger

Most recent common ancestor

In genetics, the most recent common ancestor of any set of organisms is the most recent individual from which all organisms in the group are directly Common descent....
of extant arthropod

Arthropod

Arthropods are animals belonging to the Scientific classification Arthropoda , and include the insects, arachnids, crustaceans, and others....
s , but modern arthropods have eight or fewer. It has been argued that the ancestral leg need not have been so complex, and that other events, such as the successive loss of function of a Hox-gene

Homeobox

A homeobox is a DNA sequence found within genes that are involved in the regulation of patterns of development in animals, fungus and plants. Genes that have a homeobox are called homeobox genes and form the homeobox gene family....
could result in parallel

Parallelism

Parallelism may refer to:* Angle of parallelism, the angle at one vertex of a right hyperbolic triangle that has two hyperparallel sides* Conscious parallelism, price-fixing between competitors in an oligopoly that occurs without an actual spoken agreement between the parties...
gains of leg segments.

Biramous and uniramous

The appendages of arthropods may be either biramous or uniramous. A uniramous limb comprises a single series of segments attached end-to-end. A biramous limb, however, branches into two, and each branch consists of a series of segments attached end-to-end.

The legs of insects and myriapods

Myriapoda

Myriapoda is a subphylum of arthropods containing millipedes, centipedes, and others. The group contains 13,000 species, all of which are terrestrial animal ....
are uniramous. In crustaceans, the first antennae are uniramous, but the second antennae are biramous, as are the legs in most species.

For a time, possession of uniramous limbs was believed to be a shared, derived character

Cladistics

Cladistics is the hierarchical classification of species based on evolutionary ancestry. Cladistics is distinguished from other taxonomic systems because it focuses on evolution rather than similarities between species, and because it places heavy emphasis on objective, quantitative analysis....
, so uniramous arthropods were grouped into a taxon called Uniramia

Uniramia

S. M. Manton's polyphyletic Arthropod hypothesis with Uniramia as one of three Phyla.Uniramia was one of three phyla in the classification suggested by Sidnie Manton of the Arthropoda....
. It is now believed that several groups of arthropods evolved uniramous limbs independently from ancestors with biramous limbs, so this taxon is no longer used.

Chelicerata

Spiders'

Spider

Spiders are air-breathing chelicerate arthropods that have eight legs, and chelicerae modified into fangs that inject venom. In their bodies the usual arthropod segments are fused into two Tagma , the cephalothorax and abdomen, joined by a small, cylindrical pedicel....
legs differ from those of insects by the addition of two segments on either side of the tibia, the patella between the femur and the tibia, and the metatarsus (sometimes called basitarsus) between the tibia and the tarsus (sometimes called telotarsus), making a total of seven segments.

The situation is identical in scorpion

Scorpion

Scorpions are any arachnid of the order Scorpionida. They are members of the order Scorpiones within the class Arachnida. There are about 2,000 species of scorpions, found widely distributed south of about Latitude, except New Zealand and Antarctica....
s, but with the addition of a pre-tarsus beyond the tarsus. The claws of the scorpion are not truly legs, but are pedipalp

Pedipalp

Pedipalps, are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with Mandible_ in Crustacea and insects, although more recent studies suggest they are probably homologous with the crustacean second antennae....
s, a different kind of appendage

Appendage

An appendage in the broadest sense is an additional or subsidiary part existing on, or added to, something which can generally still function if the appendage has never existed or is later provided or grown, or will still perform a primary function if the appendage is removed....
that is also found in spiders and is specialised for predation.

In Limulus
Horseshoe crab

The horseshoe crab or Atlantic horseshoe crab is a marine chelicerate arthropod. Despite its name, it is more closely related to spiders, ticks, and scorpions than to crabs....
, there are no metatarsi or pretarsi, leaving six segments per leg.

Crustacea

The legs of crustacean

Crustacean

Crustaceans are a large group of arthropods, comprising almost 52,000 described species , and are usually treated as a subphylum . They include various familiar animals, such as crabs, lobsters, crayfish, shrimp, krill and barnacles....
s are divided primitively into seven segments, which do not follow the naming system used in the other groups. They are: coxa, basis, ischium, merus, carpus, propodus, and dactylus. In some groups, some of the limb segments may be fused together. The claw

Claw

A claw is a curved, pointed appendage, found at the end of a toe or finger in most mammals, birds, and some reptiles. Somewhat similar fine hooked structures are found in arthropods such as beetles and spiders, at the end of the leg or Arthropod leg for gripping a surface as the creature walks....
of a lobster or crab is formed by the articulation of the dactylus against an outgrowth of the propodus. Crustacean limbs also differ in being biramous, whereas all other extant arthropods have uniramous limbs.

Myriapoda
Myriapoda

Myriapoda is a subphylum of arthropods containing millipedes, centipedes, and others. The group contains 13,000 species, all of which are terrestrial animal ....

Millipede

Millipedes are arthropods that have two pairs of arthropod leg per segment . Each segment that has two pairs of legs is a result of two single segments fused together as one....
s, centipede

Centipede

For information about the old arcade game, see Centipede .Centipedes are arthropods belonging to the class Chilopoda and the Subphylum Myriapoda....
s and their relatives have seven-segmented legs, comprising coxa, trochanter, prefemur, femur, tibia, tarsus, and a tarsal claw.

Arthropod leg

Biramous and uniramous

Chelicerata

Crustacea

MyriapodaMyriapodaMyriapoda is a subphylum of arthropods containing millipedes, centipedes, and others. The group contains 13,000 species, all of which are terrestrial animal ....

Myriapoda
Myriapoda

Myriapoda is a subphylum of arthropods containing millipedes, centipedes, and others. The group contains 13,000 species, all of which are terrestrial animal ....