In addition to the three living genera, Ricinulei has a fossil-record spanning over 300 million years, including fossils from the Late Carboniferous of Euramerica and the Cretaceous Burmese amber.

The most important general account of ricinuleid anatomy remains the 1904 monograph by Hans Jacob Hansen and William Sørensen.

[20] Ricinuleids inhabit the leaf litter of rainforest floors, as well as caves, where they search for prey with their elongate sensory second leg pair.

[22] Relatively little is known about their courtship and mating habits,[23] but males have been observed using their modified third pair of legs to transfer a spermatophore to the female.

The eggs are carried under the mother's hood, until the young hatch into six-legged larva, which later molt into their eight-legged adult forms.

[25] Ricinulei are unique among arachnids in that the first one to be discovered was a fossil, described in 1837 by the noted English geologist William Buckland;[26] albeit misinterpreted as a beetle.

Further fossil species were added in subsequent years by, among others, Samuel Hubbard Scudder, Reginald Innes Pocock and Alexander Petrunkevitch.

Fifteen of the twenty species of fossil ricinuleids discovered so far originate from the late Carboniferous (Pennsylvanian) coal measures of Europe and North America.

Curculioidids, by contrast, have an opisthosoma without obvious tergites, but with a single median sulcus; a dividing line running down the middle of the back.

Five species: ?Poliochera cretacea, Primoricinuleus pugio, Hirsutisoma acutiformis, H. bruckschi, H. grimaldii and H. dentata, are known from the Cenomanian (~99 million years old) Burmese amber of Myanmar;[28][29][30][31] Curculioides bohemondi, the largest of all Ricinulei, was a member of the Curculioididae.

[33] The fossil genera from the Cretaceous Burmese amber are referred to the extinct order Primoricinulei, and are thought to have had a different ecology than modern species as tree-dwelling predators that crawled on bark.

[31] As of September 2022[update], the World Ricinulei Catalog accepts the following genera:[34] In 1665, Robert Hooke described a large crab-like mite he observed with a microscope, he published a description of it in his book; Micrographia.

[35] The first living ricinuleid described using Linnaean taxonomy was from West Africa by Félix Édouard Guérin-Méneville in 1838,[36] i.e. one year after the first fossil.

This was followed by a second living example collected by Henry Walter Bates in Brazil and described by John Obadiah Westwood in 1874,[37] and a third from Sierra Leone by Tamerlan Thorell in 1892.

[38] In these early studies ricinuleids were thought to be unusual harvestmen (Opiliones), and in his 1892 paper Thorell introduced the name "Ricinulei" for these animals as a suborder of the harvestman.

[48] Characteristics shared by ricinuleids and trigonotarbids include the division of the tergites on the opisthososma into median and lateral plates and the presence of an unusual 'locking mechanism' between the two halves of the body.