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.
Ticks are parasitic arachnids of the order Ixodida. They are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Ticks are external parasites, living by feeding on the blood of mammals, birds, and sometimes reptiles and amphibians. The timing of the origin of ticks is uncertain, though the oldest known tick fossils are from the Cretaceous period, around 100 million years old. Ticks are widely distributed around the world, especially in warm, humid climates.
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.
The Acariformes, also known as the Actinotrichida, are the more diverse of the two superorders of mites. Over 32,000 described species are found in 351 families, with an estimated total of 440,000 to 929,000 species, including undescribed species.
Opilioacaridae is the sole family of mites in the order Opilioacarida, made up of about 13 genera. The mites of this family are rare, large mites, and are widely considered primitive, as they retain six pairs of eyes, and abdominal segmentation. They have historically been considered separate from other mites belonging to Acariformes and Parasitiformes, but are now generally considered a subgroup of Parasitiformes based on molecular phylogenetics.
Mesostigmata is an order of mites belonging to the Parasitiformes. They are by far the largest group of Parasitiformes, with over 8,000 species in 130 families. Mesostigmata includes parasitic as well as free-living and predatory forms. They can be recognized by the single pair of spiracles positioned laterally on the body.
Eriophyoidea are a superfamily of herbivorous mites. All post-embryonic instars lack the third and fourth pairs of legs, and the respiratory system is also absent.
Endeostigmata is a suborder of acariform mites. There are about ten families in Endeostigmata. The grouping is strongly suspected to be paraphyletic, containing unrelated early diverging lineages of mites.
The Trombidiformes are a large, diverse order of mites.
Opilioacarus is a genus of opilioacarid mites native to the Mediterranean region. The following species are recognised:
Dermanyssoidea is a superfamily of mites, including most of the mites which parasitise vertebrates.
Euryparasitus is a genus of mites in the family Ologamasidae. There are about 15 described species in Euryparasitus.
Pachylaelapidae is a family of mites in the order Mesostigmata. There are about 16 genera and more than 200 described species in Pachylaelapidae.
Rhinonyssidae is a family of mites in the order Mesostigmata. There are about 16 genera and at least 460 described species in Rhinonyssidae.
Blattisociidae is a family of mites in the order Mesostigmata.
This list of fossil arthropods described in 2018 is a list of new taxa of trilobites, fossil insects, crustaceans, arachnids, and other fossil arthropods of every kind that were described during the year 2018, as well as other significant discoveries, and events related to arthropod paleontology that are scheduled to occur in the year 2018.
Sejida is a suborder of mites in the order Mesostigmata. There are about 5 families and 13 described species in Sejida. The oldest known record of the group is an indeterminate deutonymph belonging to Sejidae from the mid Cretaceous (Albian-Cenomanian) aged Burmese amber of Myanmar.
Trigynaspida is a suborder of mites in the order Mesostigmata. There are more than 25 families and at least 90 described species in Trigynaspida.
Wolfgang Siegfried Karg (1927–2016) was an East German entomologist who specialised in mites (Acari).
Ventral views of male (left) and female (right) of Diplothyrus lecorrei (Holothyrida, Neothyridae)
Specimen of Opilioacarus baeticus (Opilioacarida)
Specimens of Nuttalliella (Ixodida, Nuttalliellidae)
