Leg of the arthropods

The Patte of the Arthropodes is a form of articulated member. Moreover, the term even of arthropod comes from the words Greek S ltr grc ἄρθρον ( arthron ), the articulation and ltr grc ποδος ( podos ), the foot, and thus means “articulated leg”.
the leg is usually used for Marcher, but of other utlisations of the member are possible (gripping, stroke…)

Many the terms used to describe the segments of the legs of arthropod derive from the Latin , and can be confused with the terms indicating the Os Tétrapodes: Coxa (meaning Hip in Latin), Trochanter , femur , patella , tibia , tarsus , Ischium , (Carp?) , dactylus (meaning Finger).
On finds sometimes the term of Procoxa to indicate the first basal segment of a forefoot (P1) at a Arthropode.

The homology between the segments of the legs between the groups is difficult to prove and it is the source of polemic.
Certains authors counts up to eleven segments per leg starting from the common ancestor most recent of the arthropods. However the modern arthropods have eight segments or less. The fact that the ancestral leg does not need to be also complex was lengthily discussed. Other events, such as the loss of successive function of a Homéobox could lead to a profit in the number of segments of the leg.

Biramé and uniramé member

The members of the arthropods can be either “biramé” or “uniramé”. A uniramé member includes/understands a simple series of end to end attached segments. A biramé member, on the other hand, is divided into two, and each branch consists of a series of end to end attached segments.

The legs of the insects and the Myriapodes are uniramées. In shellfish, the first antennas are uniramées, but the seconds are biramées, just like are to it the legs in the majority of the species.

During a time one believed that the possession of uniramés members was a shared derived character, so much so that one grouped the arthropods uniramés in a taxon called Uniramia. It is thought now that several groups of arthropods developed members uniramé independently starting from ancestors having biramés members, and thus this taxon is not used any more.

Chélicérates

Legs of the Spider S different from those of the insects by the addition of two segments, the patella between the femur and the tibia, and the métatarse (called basitarse sometimes) between the tibia and the tarsus (called sometimes télotarse then), and thus giving a total of seven segments.

The situation is identical at the scorpion S, but with the addition of a pre-tarsus beyond the tarsus. The grips of the scorpion are not really legs, but are pédipalpes , a type different of member which one finds besides also in the spiders and which is specialized for the predation.

At the gilded crabs or Limules , it does not have there a métatarse nor of prétarse, which gives a total of six segments per leg.

Mandibulates

Crustacean

The legs of the Crustacé S are divided originally into seven segments, which do not follow the system of naming used in the other groups. These segments are: Coxa , basis , ischium , merus , carpus , propodus , and dactylus . In certain groups, some of the segments of the legs can have amalgamated.
La claw of a lobster or a crab is formed by the articulation of the dactylus against an outgrowth of the propodus.
Les members of shellfish different also by the fact of being biramés, whereas all the other arthropods have uniramés members.
La first pair of these péréiopodes corresponds to the chélipèdes (" pince"), generally very developed.

Hexapodes

Insects (see Leg of insect): of uniramé type, the segmentation includes/understands a coxa , a trochanter , a femur , a tibia , a tarsus .
Collemboles : the situation is similar, with for each leg the same segmentation but with a complex forming the foot.

Myriapodes

The Millepatte S have legs with seven segments, including/understanding the coxa, the trochanter, a préfémur, the femur, the tibia, the tarsus, and tarsale scratches it.

References

Reflections one arthropod evolution in Biol. J. Flax. Plowshare B by Fryer, G., 1996, volume 58, exit 1, pages 1 to 55.
Developmental genetics and arthropod evolution: leaves I, one legacy, by Schram, F.R. & S. Koenemann, in Evolution & Development, volume 3, exit 5, pages 343 to 354,2001.

See too

Exosquelette

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