The subphylum Chelicerata constitutes one of the major subdivisions of the phylum Arthropoda. Chelicerates include the sea spiders, horseshoe crabs, and arachnids, as well as a number of extinct lineages, such as the eurypterids and chasmataspidids.
Arachnids are arthropods in the class Arachnida of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaroons.
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 reference to a lack of the flagellum that is otherwise seen in whip scorpions. Amblypygids possess no silk glands or venom. They rarely bite if threatened, but can grab fingers with their pedipalps, resulting in thorn-like puncture injuries.
Schizomida, also known as sprickets or short-tailed whip-scorpions, is an order of arachnids, generally less than 5 millimetres (0.20 in) in length. The order is not yet widely studied. E. O. Wilson has identified schizomids as among the "groups of organisms that desperately need experts to work on them."
The Opiliones are an order of arachnids colloquially known as harvestmen, harvesters, harvest spiders, or daddy longlegs. As of April 2017, over 6,650 species of harvestmen have been discovered worldwide, although the total number of extant species may exceed 10,000. The order Opiliones includes five suborders: Cyphophthalmi, Eupnoi, Dyspnoi, Laniatores, and Tetrophthalmi, which were named in 2014.
Palpigradi is an order of very small arachnids commonly known as microwhip scorpion or palpigrades.
A book lung is a type of respiration organ used for atmospheric gas exchange that is present in many arachnids, such as scorpions and spiders. Each of these organs is located inside an open ventral abdominal, air-filled cavity (atrium) and connects with its surroundings through a small opening for the purpose of respiration.
Mites are small arachnids. Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari. However, most recent genetic analyses do not recover the two as each other's closest relative within Arachnida, rendering the group non-monophyletic. Most mites are tiny, less than 1 mm (0.04 in) in length, and have a simple, unsegmented body plan. The small size of most species makes them easily overlooked; some species live in water, many live in soil as decomposers, others live on plants, sometimes creating galls, while others are predators or parasites. This last type includes the commercially destructive Varroa parasite of honey bees, as well as scabies mites of humans. Most species are harmless to humans, but a few are associated with allergies or may transmit diseases.
Pedipalps are the secondary pair of forward appendages among chelicerates – a group of arthropods including spiders, scorpions, horseshoe crabs, and sea spiders. The pedipalps are lateral to the chelicerae ("jaws") and anterior to the first pair of walking legs.
Solifugae is an order of animals in the class Arachnida known variously as camel spiders, wind scorpions, sun spiders, or solifuges. The order includes more than 1,000 described species in about 147 genera. Despite the common names, they are neither true scorpions nor true spiders. Most species of Solifugae live in dry climates and feed opportunistically on ground-dwelling arthropods and other small animals. The largest species grow to a length of 12–15 cm (5–6 in), including legs. A number of urban legends exaggerate the size and speed of the Solifugae, and their potential danger to humans, which is negligible.
Ammotrechidae is a family of solifuges distributed in the Americas and the Caribbean Islands. It includes 26 described genera and 95 species. Members of this family can be distinguished from members of other families by the absence of claws on tarsi of leg I, tarsal segmentation 1-2-2-(2-4), pedipalps with pairs of lateroventral spines, and by males having an immovable flagellum on the mesal face of each chelicerum. The propeltidium of the Ammotrechidae is recurved.
Plesiosiro is an extinct arachnid genus known exclusively from nine specimens from the Upper Carboniferous of Coseley, Staffordshire, United Kingdom. The genus is monotypic, represented only by the species Plesiosiro madeleyi described by Reginald Innes Pocock in his important 1911 monograph on British Carboniferous arachnids. It is the only known member of the order Haptopoda.
Trichobothria are elongate setae ("hairs") present in arachnids, various orders of insects, and myriapods that function in the detection of airborne vibrations and currents, and electrical charge. In 1883, Friedrich Dahl observed that they were deflected by the sound waves from a violin and labelled them 'hearing hairs'.
Tetrapulmonata is a non-ranked supra-ordinal clade of arachnids. It is composed of the extant orders Uropygi, Schizomida, Amblypygi and Araneae (spiders). It is the only supra-ordinal group of arachnids that is strongly supported in molecular phylogenetic studies. Two extinct orders are also placed in this clade, Haptopoda and Uraraneida. In 2016, a newly described fossil arachnid, Idmonarachne, was also included in the Tetrapulmonata; as of March 2016 it has not been assigned to an order.
Dromopoda is a proposed subclass of the arachnids, including the Opiliones (harvestmen), Scorpions, Pseudoscorpions and Solifugae. The latter three are sometimes grouped as Novogenuata. Combined morphological and molecular analyses have shown Dromopoda to be monophyletic. However, a strictly molecular analysis did not support the monophyly of Dromopoda.
Phalangium opilio is a species of harvestman belonging to the family Phalangiidae.
Chelypus ('clawfoot') is a genus of slow-moving, burrowing sunspiders confined to the deserts and arid regions of Southern Africa.
Solpugidae is a family of solifuges or sun spiders. Solpugidae have groups of papillae on their pedipalps or sensory organs. The papillae come out of sockets that are characterized with the function of mechanoreceptor, and contact chemoreceptors, which allows them to respond to stimuli such as touch and sound.
Chanbria is a genus of camel spiders. It consists of four species found in the Sonoran Desert in Mexico and the southwestern United States.
