The chelicerae () are the mouthparts of the subphylum

Chelicerata The subphylum Chelicerata (from Neo-Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. Chelicerates include the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, tic ...

, an

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

group that includes

arachnid Arachnids are arthropods in the Class (biology), class Arachnida () of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, opiliones, harvestmen, Solifugae, camel spiders, Amblypygi, wh ...

horseshoe crab Horseshoe crabs are arthropods of the family Limulidae and the only surviving xiphosurans. Despite their name, they are not true crabs or even crustaceans; they are chelicerates, more closely related to arachnids like spiders, ticks, and scor ...

s, and

sea spider Sea spiders are marine arthropods of the class (biology), class Pycnogonida, hence they are also called pycnogonids (; named after ''Pycnogonum'', the type genus; with the suffix '). The class includes the only now-living order (biology), order P ...

s. Commonly referred to as "

jaw The jaws are a pair of opposable articulated structures at the entrance of the mouth, typically used for grasping and manipulating food. The term ''jaws'' is also broadly applied to the whole of the structures constituting the vault of the mouth ...

s", chelicerae may be shaped as either articulated

fangs A fang is a long, pointed tooth. In mammals, a fang is a modified maxillary tooth, used for biting and tearing flesh. In snakes, it is a specialized tooth that is associated with a venom gland (see snake venom). Spiders also have external Chelic ...

, or as a type of pincers. Some chelicerae, such as those found on nearly all

spider Spiders (order (biology), order Araneae) are air-breathing arthropods that have eight limbs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude spider silk, silk. They are the largest order of arachnids and ran ...

s, are hollow and contain (or are connected to) venom glands, used to inject

venom Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...

into prey or a perceived threat. Both pseudoscorpions and harvestmen have additional structures on their chelicerae that are used for grooming (papillae in pseudoscorpions, cheliceral teeth in Opiliones). In '' Paratrechalea'', males and females have shown to have a chelicerae dimorphism, because the chelicerae is used as a mating signal for females.

Types

Chelicerae can be divided into three kinds: jackknife chelicerae, scissor chelicerae, and three-segmented

chelate Chelation () is a type of bonding of ions and their molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These l ...

chelicerae.

Jackknife chelicerae

The jackknife chelicera is subchelate (with fixed finger much reduced or absent) and is composed of two segments. This type of chelicera occurs exclusively in the

Tetrapulmonata Tetrapulmonata is a Taxonomic rank, non-ranked Order (biology), supra-ordinal clade of arachnids. It is composed of the Extant taxon, extant orders Uropygi (whip scorpions), Schizomida (short-tailed whip scorpions), Amblypygi (tail-less whip scor ...

. Jackknife chelicera are described in two different forms: orthognathous and labidognathous. Orthognathous chelicerae are articulated in a manner that enables movements of the appendages parallel to the body axis. This kind of chelicera occurs in the Liphistiomorphae and

Mygalomorphae The Mygalomorphae, or mygalomorphs, are an infraorder of spiders, and comprise one of three major groups of living spiders with over 3,000 species, found on all continents except Antarctica. Many members are known as trapdoor spiders due to t ...

spiders and in the related orders

Amblypygi Amblypygi is an order of arachnids also known as whip-spiders or tailless whip-scorpions, not to be confused with whip-scorpions or vinegaroons that belong to the related order Thelyphonida. The name "amblypygid" means "blunt tail", a referen ...

Schizomida Schizomida, also known as sprickets or short-tailed whip-scorpions, is an order of arachnids, generally less than in length. The order is not yet widely studied. E. O. Wilson has identified schizomids as among the "groups of organisms that des ...

and

Uropygi Uropygi is an arachnid order comprising invertebrates commonly known as whip scorpions or vinegaroons (also spelled vinegarroons and vinegarones). They are often called uropygids. The name "whip scorpion" refers to their resemblance to scorpion ...

. Labidognathous chelicerae move at right angles to the body axis. This kind of chelicera is rotated and occurs exclusively in the

Araneomorphae The Araneomorphae (also called the Labidognatha or "true spiders") are an infraorder of spiders. They are distinguishable by chelicerae (fangs) that point diagonally forward and cross in a pinching action, in contrast to the Mygalomorphae (taran ...

spiders.

Spider chelicerae

The chelicerae consist of a base segment, sometimes called the "paturon", that articulates with the

cephalothorax The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''cepha ...

(or

prosoma The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''cepha ...

) and a

fang A fang is a long, pointed tooth. In mammals, a fang is a modified maxillary tooth, used for biting and tearing flesh. In snakes, it is a specialized tooth that is associated with a venom gland (see snake venom). Spiders also have external fangs, ...

portion that articulates with the base segment. Almost all spiders have venom glands and can inject the venom through openings near the tips of their fangs when

biting Biting is an action involving a set of teeth closing down on an object. It is a common zoological behavior, being found in toothed animals such as mammals, reptiles, amphibians, fishes, and arthropods. Biting is also an action humans participate ...

prey. The glands that produce this venom are located in the two segments of the chelicerae, and, in most spiders, extend beyond the chelicerae and into the cephalothorax. The fang, the organic functional equivalent to a

hypodermic needle A hypodermic needle (from Greek Language, Greek ὑπο- (''hypo-'' = under), and δέρμα (''derma'' = skin)) is a very thin, hollow tube with one sharp tip. As one of the most important intravenous inventions in the field of drug admini ...

is what penetrates the skin, fur, or exoskeleton of the spider's target—spider mouthparts are primarily intended for envenoming a spider's prey in most species, typically

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

s and other small

s. The basal portion includes all or part of the spider's venom glands, which can be squeezed to control the amount of venom forced out of the glands. Such control permits a spider to administer either a

dry bite A dry bite is a bite by a venomous animal in which no venom is released. Dry snake bites are called "venomous snake bite without envenoming". A dry bite from a snake can still be painful, and be accompanied by bleeding, inflammation, swelling and/o ...

, a dose appropriate to the nature of the prey or enemy, or a maximal dose. The control is also necessary for actions such as the spitting of venomous silk by members of the family Scytodidae; they depend on that mechanism both in hunting and defence. When a spider bites, the two parts of the chelicerae come together like a folding knife, and when making a threat display or actually preparing to bite, the spider will open the angle of the fangs with the basal portion of the ''chelicerae'' and also open the angle of the basal portion with the cephalothorax. In the tarantulas and other

, the horizontal separation of the tips of the fangs does not change much, but in the other spiders the tips of the fangs move apart from each other as well as elevating. Even the tips of the fangs of the rather large spider shown above are quite sharp, and the spider's body is well adapted to driving the fangs into flesh. Some spider bites, such as those of the

Sydney funnel-web spider The Sydney funnel-web spider (''Atrax robustus'') is a species of venomous Mygalomorphae, mygalomorph spider native to eastern Australia, usually found within a radius of Sydney. It is a member of a group of spiders known as Australian funnel- ...

, are reported to have penetrated toenails and soft leather shoes.

Uncate chelicerae

850 8879 Solifugae.jpg, Uncate chelicerae of a solifuge Anterior view of Loxosceles reclusa (Brown Recluse Spider) (22830337766).jpg, Front view of a brown recluse spider, showing its chelicerae Pseudoscorpion (7586033338).jpg, Uncate chelicerae of a pseudoscorpion The uncate chelicera is chelate and composed of two segments and occurs in the orders Pseudoscorpiones,

Solifugae Solifugae is an Order (biology), order of Arachnid, arachnids known variously as solifuges, sun spiders, camel spiders, and wind scorpions. The order includes more than 1,000 described species in about 147 genus, genera. Despite the common names, ...

Ricinulei Ricinulei is a small order of arachnids. Like most arachnids, they are predatory; eating small arthropods. They occur today in west-central Africa ('' Ricinoides'') and the Americas ('' Cryptocellus'' and '' Pseudocellus'') from Brazil to southern ...

, and

Araneae Spiders ( order Araneae) are air-breathing arthropods that have eight limbs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...

(e.g., brown recluse, cellar spider, and crevice weaving spider).

Three-segmented chelate chelicerae

Limulus polyphemus 201780311 (cropped).jpg, Three-segmented chelicerae of an

Atlantic horseshoe crab The Atlantic horseshoe crab (''Limulus polyphemus''), also known as the American horseshoe crab, is a species of horseshoe crab, a kind of marine biology, marine and Brackish water, brackish chelicerate arthropod. It is found in the Gulf of Mexic ...

Pantopsalis albipalpis 1276804.jpg, '' Pantopsalis albipalpis'', a species of harvestman with exceptionally long three-segmented chelicerae Acutiramus cummingsi (YPM IP 018609).jpg, Isolated fossil chelicera of a pterygotid

eurypterid Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the Order (biology), order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period, 467.3 Myr, mil ...

, '' Acutiramus cummingsi'' Having three-segmented chelate chelicerae is the primitive condition and occurs in

s such as the

Scorpion Scorpions are predatory arachnids of the Order (biology), order Scorpiones. They have eight legs and are easily recognized by a pair of Chela (organ), grasping pincers and a narrow, segmented tail, often carried in a characteristic forward cur ...

es and the

Opiliones The Opiliones (formerly Phalangida) are an Order (biology), order of arachnids, Common name, colloquially known as harvestmen, harvesters, harvest spiders, or daddy longlegs (see below). , over 6,650 species of harvestmen have been discovered w ...

, as well as in non-arachnid Chelicerata such as the

Xiphosura Xiphosura (; , in reference to its sword-like telson) is an order of arthropods related to arachnids. They are more commonly known as horseshoe crabs (a name applied more specifically to the only extant family, Horseshoe crab, Limulidae). They fir ...

and

Eurypterida Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period, 467.3 million years ago. The ...

. The chelifores of the

Pycnogonida Sea spiders are marine arthropods of the class Pycnogonida, hence they are also called pycnogonids (; named after ''Pycnogonum'', the type genus; with the suffix '). The class includes the only now-living order Pantopoda ( ‘all feet’), alongs ...

may be homologous to chelicerae.

References

External links

* {{Spider nav Chelicerate anatomy