Pedipalps are the second pair of appendage

Appendage

In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...

s of the prosoma in the subphylum Chelicerata

Chelicerata

The subphylum Chelicerata constitutes one of the major subdivisions of the phylum Arthropoda, and includes horseshoe crabs, scorpions, spiders and mites...

. They are traditionally thought to be homologous with mandibles

Mandible (arthropod)

thumb|250px|The mandibles of a [[Bull ant]]The mandible of an arthropod is either of a pair of mouthparts used for biting, cutting and holding food. Mandibles are often simply referred to as jaws. Mandibles are present in the extant subphyla Myriapoda , Crustacea and Hexapoda...

 in Crustacea and insects, although more recent studies (e.g. using Hox genes) suggest they are probably homologous with the crustacean second antennae.

Chelicerate pedipalps are appendages of six articles: the coxae, a single trochanter, the femur

Femur

The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...

, a short patella, the 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....

, and the tarsus

Tarsus (skeleton)

In tetrapods, the tarsus is a cluster of articulating bones in each foot situated between the lower end of tibia and fibula of the lower leg and the metatarsus. In the foot the tarsus articulates with the bones of the metatarsus, which in turn articulate with the bones of the individual toes...

. In spiders the coxae frequently have extensions called maxillae or gnathobases, which function as mouth

Mouth

The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth....

 parts with or without some contribution from the coxae of the anterior legs

Arthropod leg

The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments are of Latin origin, and may be confused with terms for bones: coxa , trochanter , femur, tibia, tarsus, ischium, metatarsus, carpus, dactylus ,...

. The limbs themselves may be simple tactile organs outwardly resembling the legs, as in spider

Spider

Spiders are air-breathing arthropods that have eight legs, and chelicerae with fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms...

s, or chelate weapons of great size, as in the scorpion

Scorpion

Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...

s. Comparative studies of pedipalpal morphology may suggest that leg-like pedipalps are primitive in Arachnida. At present, the only reasonable alternative to this view is to assume that xiphosurans reflect the morphology of the primitive arachnid

Arachnid

Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...

 pedipalp and to conclude that this appendage is primitively chelate. Chelate or sub chelate pedipalps are found in several arachnid

Arachnid

Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...

 groups, i.e. Ricinulei

Ricinulei

The Order Ricinulei is a group of arachnids known as hooded tickspiders. In older works they are sometimes referred to as Podogona., 60 extant species of ricinuleids have been described worldwide, all in the single family Ricinoididae. They occur today in west-central Africa and the Neotropical...

, Thelyphonida, Scorpiones and Pseudoscorpiones, but the chelae in most of these taxa may not be homologous with those found in Xiphosura

Xiphosura

Xiphosura is an order of marine chelicerates which includes a large number of extinct lineages and only four recent species in the family Limulidae, which include the horseshoe crabs...

. The pedipalps are distinctly raptorial

Raptorial

The term raptorial implies much the same as "predatory", but most often refers to modifications of an arthropod's foreleg that make it function for the grasping of prey while it is consumed, where the gripping surfaces are formed from the opposing faces of two successive leg segments...

 in Amblypygi, Thelyphonida, Schizomida and some Opiliones

Opiliones

Opiliones are an order of arachnids commonly known as harvestmen. , over 6,400 species of harvestmen have been discovered worldwide, although the real number of extant species may exceed 10,000. The order Opiliones can be divided into four suborders: Cyphophthalmi, Eupnoi, Dyspnoi and Laniatores...

 belonging to the laniatorid group.

Spider pedipalps

Pedipalps of spiders have the same segmentation as the legs

Arthropod leg

The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments are of Latin origin, and may be confused with terms for bones: coxa , trochanter , femur, tibia, tarsus, ischium, metatarsus, carpus, dactylus ,...

, but the tarsus

Tarsus (skeleton)

In tetrapods, the tarsus is a cluster of articulating bones in each foot situated between the lower end of tibia and fibula of the lower leg and the metatarsus. In the foot the tarsus articulates with the bones of the metatarsus, which in turn articulate with the bones of the individual toes...

 is undivided, and the pretarsus has no lateral claws. In sexually mature male spiders, the final segment of the pedipalp, the tarsus, develops into a complicated structure (sometimes called the palpal organ or bulb) that is used to transfer sperm to the female seminal receptacles during mating. The details of this structure vary considerably between different groups of spiders and are useful for identifying species.

The cymbium is a spoon-shaped structure located at the end of the spider pedipalp which supports the palpal organ. The cymbium may also be used as a stridulatory organ in spider courtship.

External links

• Several close-up photos of a tarantula creating a sperm web - Brachypelma Vagans (Mexican Red-rump)