The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. 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 Arthropods are Animals belonging to the Phylum Arthropoda (from Greek ἄρθρον arthron, " Joint " Walking (also called ambulation) is the main form of Animal Locomotion on land, distinguished from Running and crawling Many of the terms used for arthropod leg segments are of Latin origin, and may be confused with terms for bones: coxa (meaning hip), trochanter (compare greater trochanter and lesser trochanter), femur, tibia, tarsus, ischium, metatarsus, carpus, dactylus (meaning finger), patella. Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. The greater trochanter (great trochanter of the Femur is a large irregular quadrilateral eminence The lesser trochanter (small trochanter of the Femur is a conical eminence which varies in size in different subjects It projects from the lower and back part of the base The femur is the thigh bone In Humans, it is the longest, most voluminous and strongest Bone. The tibia, shinbone, or shankbone is the larger and stronger of the two Bones in the Leg below the Knee in vertebrates and connects In Tetrapods the tarsus are the cluster of Bones in the Foot between the Tibia and Fibula and the Metatarsus. The ischium forms the lower and back part of the Hip bone ( os coxae) The metatarsus consists of the five long Bones of the Foot, which are numbered from the medial side ( ossa metatarsalia I In Tetrapods the carpus is the sole cluster of the Bones in the Wrist between the radius and Ulna and the Metacarpus 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 The patella or kneecap 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. Some authors posit up to eleven segments per leg for the most recent common ancestor of extant arthropods ^[1], but modern arthropods have eight or fewer. In Genetics, the most recent common ancestor ( MRCA) of any set of Organisms is the most recent individual from which all organisms in the group are directly Arthropods are Animals belonging to the Phylum Arthropoda (from Greek ἄρθρον arthron, " Joint " It has been argued ^[2][3] 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 could result in parallel gains of leg segments. A homeobox is a DNA sequence found within Genes that are involved in the regulation of patterns of development ( Morphogenesis) in Animals

Biramous and uniramous

Crustacean appendages

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 are uniramous. Myriapoda is a Subphylum of Arthropods containing Millipedes Centipedes and others 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, so uniramous arthropods were grouped into a taxon called Uniramia. Cladistics is the hierarchical classification of Species based on evolutionary ancestry S M Manton's (1973 polyphyletic Arthropod hypothesis with Uniramia as one of three Phyla 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.

Hexapoda

Diagram of an insect leg

The legs of insects are always found on the thorax. Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described The thorax is a division of an Animal 's body that lies between the head and the Abdomen. They have five segments per leg (coxa, trochanter, femur, tibia, tarsus), with the tarsus being divided into several sub-sections called tarsomeres. In some groups, the number of tarsomeres is important for identification to family level, for example beetles (Coleoptera), or to subfamily level among some dipteran flies (e. In Biological classification, family ( Latin Beetles are the group of Insects with the largest number of known Species. In Biological classification, family ( Latin True flies are Insects of the Order Diptera ( Greek: di = two and pteron = wing possessing a single pair of g. Cecidomyiidae). Cecidomyiidae (sometimes misspelled Cecidomyidae) is a family of flies (Order Diptera) known as gall midges or gall gnats. Tarsal claws, also called ungues (singular: unguis), may also be present ^[4][5].

The segmentation is similar in collembolans, in which each leg has a coxa, trochanter, femur, tibia, and a foot-complex. Springtails ( Collembola) form the largest of the three lineages of modern hexapods that are no longer considered Insects (the other two are the

In addition there is a sixth segment called pretarsus, which consists of claws and various other structures on the end of the tarsus. A pad or lobe-like structure is called an arolium when it is located between the claws, as in the case of Orthoptera (grasshoppers and crickets), or pulvillus if it is located at the base of the claws, as in Diptera (flies). The Orthoptera (from the Greek ορθός orthos = "straight" and πτεрόν pteron = "wing" are an order of Insects Grasshoppers are Insects of the suborder Caelifera in the order Orthoptera. Crickets, family Gryllidae (also known as "true crickets" are Insects somewhat related to Grasshoppers and more closely related to katydids True flies are Insects of the Order Diptera ( Greek: di = two and pteron = wing possessing a single pair of True flies are Insects of the Order Diptera ( Greek: di = two and pteron = wing possessing a single pair of These structures usually serve to increase adherence on various surfaces (as for the flies) and/or to cushion a fall, such as the jump of a grasshopper.

Insects' legs are attached to the three thoracic segments, the prothorax, mesothorax and metathorax. This terminology is also sometimes applied to the leg segments, so that the mesofemur is the femur of the second pair of legs, and the protarsus is the tarsus of the first pair of legs.

Chelicerata

Diagram of a spider, with the leg segments colour-coded: coxa=grey, trochanter=red, femur=green, patella=blue, tibia=purple, metatarsus=brown, tarsus=cyan

Spiders' legs differ from those of insects by the addition of two segments, 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. Spiders are Predatory Invertebrate Animals that have two body segments, eight legs no chewing mouth parts and no wings

The situation is identical in scorpions, but with the addition of a pre-tarsus beyond the tarsus. Scorpions are eight-legged Carnivorous Arthropods They are members of the order Scorpiones within the class Arachnida. 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. Pedipalps, are the second pair of Appendages of the Prosoma in the subphylum Chelicerata. 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

In Limulus, there are no metatarsi or pretarsi, leaving six segments per leg. The horseshoe crab or Atlantic horseshoe crab ( Limulus polyphemus) is a marine Chelicerate Arthropod.

Crustacea

The leg of a squat lobster, showing the segments; the ischium and merus are fused in many decapods. Squat lobsters are decapod Crustaceans of the families Galatheidae and Chirostylidae including the common genera Galathea and The decapods or Decapoda ( literally means "ten footed") are an order of Crustaceans within the class Malacostraca, including many

The legs of crustaceans are divided primitively into seven segments, which do not follow the naming system used in the other groups. Structure of crustaceans As Arthropods crustaceans have a stiff Exoskeleton, which must be shed to allow the animal to grow ( Ecdysis or molting They are: coxa, basis, ischium, merus, carpus, propodus, and dactylus. In some groups, some of the limb segments may be fused together. The claw of a lobster or crab is formed by the articulation of the dactylus against an outgrowth of the propodus. A claw is a curved pointed appendage found at the end of a toe or finger in most Mammals, Birds, and some Reptiles. Crustacean limbs also differ in being biramous, whereas all other extant arthropods have uniramous limbs.

Myriapoda

Millipedes, centipedes and their relatives have seven-segmented legs, comprising coxa, trochanter, prefemur, femur, tibia, tarsus, and a tarsal claw. Myriapoda is a Subphylum of Arthropods containing Millipedes Centipedes and others Millipedes (Class Diplopoda, previously also known as Chilognatha are Arthropods that have two pairs of legs per segment (except for the first segment behind Centipedes (from Latin prefix centi-, "hundred" and Greek ποδός podos, " Foot " are

References

1. ^ Kukalova-Peck, J. (1992). The "Uniramia" do not exist - the ground plan of the Pterygota as revealed by Permian Diaphanopterodea from Russia (Insecta, Paleodictyopteroidea). Canadian Journal of Zoology - Revue Canadienne de Zoologie 70 (2): 236–255.  
2. ^ Fryer, G. (1996). Reflections on arthropod evolution. Biol. J. Linn. Soc. B 58 (1): 1–55.  
3. ^ Schram, F. R. & S. Frederick Robert Schram (born August 11, 1943 in Chicago, Illinois) is an American Palaeontologist and Carcinologist Koenemann (2001). Developmental genetics and arthropod evolution: part I, on legs. Evolution & Development 3 (5): 343–354. doi:10.1046/j.1525-142X.2001.01038.x. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
4. ^ Harbach, R. E. & K. L. Knight (1980). Taxonomist's Glossary of Mosquito Anatomy. Plexus, Marlton, NJ.  
5. ^ Richards, O. W. & R. G. Davies (1977). Imm's General Textbook of Entomology, 10th ed. (2 Volumes). Chapman and Hall, London.