Opilioacariformes is the smallest order

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 (or superorder) of mite

Mite

Mites, along with ticks, are small arthropods belonging to the subclass Acari and the class Arachnida. The scientific discipline devoted to the study of ticks and mites is called acarology.-Diversity and systematics:...

s, containing a single family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

, and around 10 genera

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

. They are rare, large mites, and are widely considered primitive, as they retain six pairs of eye

Eye

Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...

s, and abdominal segmentation. Opilioacariformes may be the sister group to the Parasitiformes

Parasitiformes

The Parasitiformes are a superorder of Acari . Many species are parasitic , but not all; for example, about half of the 10,000 known species in the suborder Mesostigmata are predatory and cryptozoan, living in the soil-litter, rotting wood, dung, carrion, nests or house dust...

.

The first member of the Opilioacariformes to be discovered was the Algeria

Algeria

Algeria , officially the People's Democratic Republic of Algeria , also formally referred to as the Democratic and Popular Republic of Algeria, is a country in the Maghreb region of Northwest Africa with Algiers as its capital.In terms of land area, it is the largest country in Africa and the Arab...

n species Opilioacarus segmentatus, which was described by Carl Johannes With

Carl Johannes With

Carl Johannes With was a Danish doctor and arachnologist, specialising in pseudoscorpions and mites.-Biography:...

 in 1902, followed by the Sicilian

Sicily

Sicily is a region of Italy, and is the largest island in the Mediterranean Sea. Along with the surrounding minor islands, it constitutes an autonomous region of Italy, the Regione Autonoma Siciliana Sicily has a rich and unique culture, especially with regard to the arts, music, literature,...

 Eucarus italicus and Eucarus arabicus from Aden

Aden

Aden is a seaport city in Yemen, located by the eastern approach to the Red Sea , some 170 kilometres east of Bab-el-Mandeb. Its population is approximately 800,000. Aden's ancient, natural harbour lies in the crater of an extinct volcano which now forms a peninsula, joined to the mainland by a...

, both in 1904. A single fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 specimen is known, which was discovered in Baltic amber

Baltic amber

The Baltic region is home to the largest known deposit of amber, called Baltic amber or succinite, with about 80% of the world's known amber found there. It dates from 44 million years ago...

 from the Eocene

Eocene

The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

.

• Adenacarus Hammen, 1966
• Caribeacarus Vázquez & Klompen, 2009
• Indiacarus Das & Bastawade, 2007
• Neocarus Chamberlin & Mulauk, 1942
• Opilioacarus
  Opilioacarus
  Opilioacarus is a genus of mites, containing the following species:*Opilioacarus bajacalifornicus Vázquez & Klompen, 2002*Opilioacarus italicus *Opilioacarus nicaraguensis Vázquez & Klompen, 2002...
  
  With, 1902
• Panchaetes Naudo, 1963
• Paracarus Chamberlin & Mulauk, 1942
• Phalangioacarus Coineau & Hammen, 1979
• Salfacarus Hammen, 1977
• Siamacarus Leclerc, 1989
• Vanderhammenacarus Leclerc, 1989