Ricinulei

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Ricinulei
Temporal range: Late Carboniferous–Recent
Cryptocellus goodnighti.jpg
Cryptocellus goodnighti
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Ricinulei
Thorell, 1876
Family: Ricinoididae
Ewing, 1929
Exant genera

For fossil genera, see text

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 ) as far north as Texas. As of 2021, 91 extant species of ricinuleids have been described worldwide, all in the single family Ricinoididae. [1] In older works they are sometimes referred to as Podogona. Due to their obscurity they do not have a proper common name, though in academic literature they are occasionally referred to as hooded tickspiders.

Contents

In addition to the three living genera, there are fossil species from the upper Carboniferous of Euramerica and the Cretaceous Burmese amber.

Description

The most important general account of ricinuleid anatomy remains the 1904 monograph by Hans Jacob Hansen and William Sørensen. [2] Useful further studies can be found in, e.g., the work of Pittard and Mitchell, [3] Gerald Legg [4] [5] and L. van der Hammen. [6]

Ricinoides atewa nymph from Ghana Ricinulei from Fernandez & Giribet, nymph of Ricinoides atewa (2015) (cropped).jpg
Ricinoides atewa nymph from Ghana

Body

Ricinulei are typically about 5 to 10 millimetres (0.2 to 0.4 in) long. The largest of ever existed Ricinulei was the Late Carboniferous Curculioides bohemondi with a body length of 21.77 mm (0.857 in). [7] The cuticle (or exoskeleton) of both the legs and body is remarkably thick. [8] Their most notable feature is a "hood" (or cucullus) which can be raised and lowered over the head. When lowered, it covers the mouth and the chelicerae. Living ricinuleids have no eyes, although two pairs of lateral eyes can be seen in fossils and even living species retain light-sensitive areas of cuticle in this position.

The heavy-bodied abdomen (or opisthosoma) exhibits a narrow pedicel, or waist, where it attaches to the prosoma. Curiously, there is a complex coupling mechanism between the prosoma and opisthosoma. The front margin of the opisthosoma tucks into a corresponding fold at the back of the carapace. The advantages of this unusual system are not well understood, and since the genital opening is located on the pedicel (another rather unusual feature) the animals have to 'unlock' themselves in order to mate. The abdomen is divided dorsally into a series of large plates or tergites, each of which is subdivided into a median and lateral plate.

Male Ricinoides karschii from Campo Reserve, Cameroon Ricinulei from Fernandez & Giribet, male Ricinoides karschii from Campo Reserve, Cameroon (2015) (cropped).jpg
Male Ricinoides karschii from Campo Reserve, Cameroon

Appendages

The mouthparts, or chelicerae, are composed of 2 segments forming a fixed and a moveable digit. Sensory organs are also found associated with the mouthparts; [9] presumably for tasting the food. The chelicerae can be retracted and at rest they are normally hidden beneath the cucullus.

Ricinuleid pedipalps are complex appendages. They are typically used to manipulate food items, but also bear many sensory structures and are used as 'short range' sensory organs. [10] The pedipalps end in pincers that are small relative to their bodies, when compared to those of the related orders of scorpions and pseudoscorpions. Similar pincers on the pedipalps have now been found in the extinct order Trigonotarbida (see Relationships).

As in many harvestmen, the second pair of legs is longest in ricinuleids and these limbs are used to feel ahead of the animal, almost like antennae. If the pedipalps are 'short range' sensory organs, the second pair of legs are the corresponding 'long range' ones. Sensilla on the tarsi at the ends of legs I and II (which are used more frequently to sense the surroundings) differ from those of legs III and IV. [11] [12] In male ricinuleids, the third pair of legs are uniquely modified to form copulatory organs. The shape of these organs is very important for taxonomy and can be used to tell males of different species apart. [13]

Internal anatomy

An older summary of ricinuleid internal anatomy was published by Jacques Millot. [14] The midgut has been described, [15] while the excretory system consists of Malpighian tubules and a pair of coxal glands. Female ricinuleids have spermathecae, [16] presumably to store sperm. The male genitalia, sperm cells and sperm production have also been intensively studied. [17] [18] Gas exchange takes place through trachea, and opens through a single pair of spiracles on the prosoma. [19] At least one Brazilian species appears to have a plastron, which may help it prevent getting wet and allow it to continue to breathe, even if inundated with water. [20]

Biology

Male Pseudocellus pearsei from Grutas Tzabnah, Yucatan, Mexico Ricinulei from Fernandez & Giribet, male Pseudocellus pearsei from Grutas Tzabnah, Yucatan, Mexico (2015) (cropped).jpg
Male Pseudocellus pearsei from Grutas Tzabnah, Yucatán, Mexico

Ricinuleids inhabit the leaf litter of rainforest floors, as well as caves, where they search for prey with their elongate sensory second leg pair. [21] Ricinulei feed on other small invertebrates, although details of their natural prey are sparse. [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. The six-legged larva is a feature they share with Acari (see Relationships). Despite the scarce number of studies about the biology of this group, recent studies have reported nocturnal habits, as well as novel behaviors for this group, which include interactions between individuals different than mating. [24] Ricinuleids are often found in large congregations, the exact purpose of which is unknown. [25]

Fossil record

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. They were revised in detail in 1992 by Paul Selden, [27] who placed them in a separate suborder, Palaeoricinulei. The fossils are divided into four families: Curculioididae, Poliocheridae, Primoricinuleidae and Sigillaricinuleidae. The poliocherids are more like modern ricinuleids in having an opisthosoma with a series of three large, divided tergites. 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. This superficially resembles the elytra of a beetle and explains why Buckland originally misidentified the first fossil species. 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. [7] Monooculricinuleus incisus and M. semiglobosus from Burmese amber were originally described as members of Ricinulei, but they might belong to Opiliones instead. [32]

Some Carboniferous genera of Palaeoricinulei exceed modern Ricinulei in size, with bodies 24 millimetres (0.94 in) in length, and many appear to have borne eyes, unlike modern representatives which are completely blind. It is likely they had a surface dwelling ecology unlike that of modern Ricinulei. [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]

Genera

As of September 2022, the World Ricinulei Catalog accepts the following eleven genera: [34]

Relationships

 

Acari

Palpigradi

Pycnogonida

†Trigonotarbida

Ricinulei

Araneae

Amblypygi

Uropygi

Schizomida

Cladogram showing Ricinulei
among other arachnids,
after Giribet et al. (2002). [35]

Early work

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 . [36] The first living ricinuleid described using Linnaean taxonomy was from West Africa by Félix Édouard Guérin-Méneville in 1838, [37] 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, [38] and a third from Sierra Leone by Tamerlan Thorell in 1892. [39] 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. Ricinuleids were subsequently recognized as an arachnid order in their own right in the 1904 monograph by Hansen & Soerensen. These authors recognised a group called "Arachnida micrura", comprising spiders, whip spiders, whip scorpions and ricinuleids, which they defined as having a rather narrow join between the prosoma and opisthosoma and a small 'tail end' to the opisthosoma.

Ricinuleids and mites

Morphological studies of arachnid relationships have largely concluded that ricinuleids are most closely related to Acari (mites and ticks) though more recent phylogenomic studies refute this. [40] [41] L. van der Hammen placed ricinuleids in a group called "Cryptognomae", [42] together with the anactinotrichid mites only. Peter Weygoldt and Hannes Paulus referred to ricinuleids and all mites as "Acarinomorpha". [43] [44] Jeffrey Shultz used the name "Acaromorpha". [45] [46] This hypothesis recognizes that both ricinuleids and mites hatch with a larval stage with only six legs, rather than the usual eight seen in arachnids. The additional pair of legs appears later during development. Some authors have also suggested that the gnathosoma, a separate part of the body bearing the mouthparts, is also a unique character for ricinuleids and mites, [47] but this feature is rather complex and difficult to interpret and other authors would restrict the presence of a gnathosoma sensu stricto to mites only.

Ricinuleids and trigonotarbids

In 1892, Ferdinand Karsch suggested that ricinuleids were the last living descendants of the extinct arachnid order Trigonotarbida. [48] This hypothesis was widely overlooked, but was reintroduced by Jason Dunlop in 1996. [49] 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. A further study subsequently recognised that the tip of the pedipalp in both ricinuleids and trigonotarbids ends in a similar small claw. [50] Ricinuleids as sister group of trigonotarbids was also recovered in the 2002 study by Gonzalo Giribet and colleagues. [35]

Phylogenomic studies

Recent phylogenomic studies have recovered different relationships than those previously suggested. An analysis in early 2019 suggested the sister group of the ricinuleids may be Xiphosura, the arthropod order containing horseshoe crabs. [40] In response to this work, a more recent study placed Ricinulei and Opiliones as sister taxa. [51]

Related Research Articles

<span class="mw-page-title-main">Chelicerata</span> Subphylum of arthropods

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.

<span class="mw-page-title-main">Arachnid</span> Class of arthropods

Arachnida is a class of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaroons.

<span class="mw-page-title-main">Pseudoscorpion</span> Order of arachnids

Pseudoscorpions, also known as false scorpions or book scorpions, are small, scorpion-like arachnids belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida.

<span class="mw-page-title-main">Amblypygi</span> Order of arachnids comprising whip spiders and tailless whip scorpions

Amblypygi is an order of arachnid chelicerate arthropods also known as whip spiders or tailless whip scorpions. 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 venomous fangs. They rarely bite if threatened, but can grab fingers with their pedipalps, resulting in thorn-like puncture injuries.

<span class="mw-page-title-main">Schizomida</span> Order of short-tailed whip-scorpions

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."

<span class="mw-page-title-main">Opiliones</span> Order of arachnids (harvestmen/daddy longlegs)

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.

<span class="mw-page-title-main">Xiphosura</span> Order of marine chelicerates

Xiphosura is an order of arthropods related to arachnids. They are more commonly known as horseshoe crabs. They first appeared in the Hirnantian. Currently, there are only four living species. Xiphosura contains one suborder, Xiphosurida, and several stem-genera.

<span class="mw-page-title-main">Opilioacaridae</span> Order of mites

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.

<span class="mw-page-title-main">Trigonotarbida</span> Extinct order of arachnids

The order Trigonotarbida is a group of extinct arachnids whose fossil record extends from the late Silurian to the early Permian. These animals are known from several localities in Europe and North America, as well as a single record from Argentina. Trigonotarbids can be envisaged as spider-like arachnids, but without silk-producing spinnerets. They ranged in size from a few millimetres to a few centimetres in body length and had segmented abdomens (opisthosoma), with the dorsal exoskeleton (tergites) across the backs of the animals' abdomens, which were characteristically divided into three or five separate plates. Probably living as predators on other arthropods, some later trigonotarbid species were quite heavily armoured and protected themselves with spines and tubercles. About seventy species are currently known, with most fossils originating from the Carboniferous coal measures.

<span class="mw-page-title-main">Tetrapulmonata</span> Clade of arachnids

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.

<span class="mw-page-title-main">Archaeidae</span> Family of spiders

Archaeidae, also known as assassin spiders and pelican spiders, is a spider family with about ninety described species in five genera. It contains small spiders, ranging from 2 to 8 millimetres long, that prey exclusively on other spiders. They are unusual in that they have "necks", ranging from long and slender to short and thick. The name "pelican spider" refers to these elongated jaws and necks used to catch their prey. Living species of Archaeidae occur in South Africa, Madagascar and Australia, with the sister family Mecysmaucheniidae occurring in southern South America and New Zealand.

<span class="mw-page-title-main">Evolution of spiders</span> Origin from a chelicerate ancestor and diversification of spiders through geologic time

The evolution of spiders has been ongoing for at least 380 million years. The group's origins lie within an arachnid sub-group defined by the presence of book lungs ; the arachnids as a whole evolved from aquatic chelicerate ancestors. More than 45,000 extant species have been described, organised taxonomically in 3,958 genera and 114 families. There may be more than 120,000 species. Fossil diversity rates make up a larger proportion than extant diversity would suggest with 1,593 arachnid species described out of 1,952 recognized chelicerates. Both extant and fossil species are described annually by researchers in the field. Major developments in spider evolution include the development of spinnerets and silk secretion.

<i>Mongolarachne</i> Extinct genus of spiders

Mongolarachne is an extinct genus of spiders placed in the monogeneric family Mongolarachnidae. The genus contains only one species, Mongolarachne jurassica, described in 2013, which is presently the largest fossilized spider on record. The type species was originally described as Nephila jurassica and placed in the living genus Nephila which contains the golden silk orb-weavers.

The Panther Mountain Formation is a geologic formation in New York. It preserves fossils dating back to the Devonian period. It is located in the counties of Albany, Madison, Oneida, Otsego, and Schoharie. It is well known for its fossil arthropods preserved as flattened cuticles, including Attercopus and Dracochela.

This list of fossil arthropods described in 2015 is a list of new taxa of trilobites, fossil insects, crustaceans, arachnids and other fossil arthropods of every kind that have been described during the year 2015. The list only includes taxa at the level of genus or species.

<i>Pseudocellus</i> Genus of spider-like animals

Pseudocellus is an arachnid genus in the order Ricinulei, first described by Norman Platnick in 1980. It is native to the Neotropics.

<i>Pseudocellus pearsei</i> Species of spider-like animal

Pseudocellus pearsei is an arachnid species in the order Ricinulei. It occurs in caves in Yucatan, Mexico.

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.

<span class="mw-page-title-main">Subcapitulum</span>

The subcapitulum, also known as infracapitulum, hypognathum or hipognatum, refers to the ventral part of the gnathosoma or the fusion of the palpal coxae and the labrum complex present in some arthropods on which the mouth, pedipalps, mouthparts and pharynx are generally located. It is delimited by the subcapitular apodeme, which separates it from the cheliceral frame.

Burmese amber is fossil resin dating to the early Late Cretaceous Cenomanian age recovered from deposits in the Hukawng Valley of northern Myanmar. It is known for being one of the most diverse Cretaceous age amber paleobiotas, containing rich arthropod fossils, along with uncommon vertebrate fossils and even rare marine inclusions. A mostly complete list of all taxa described up until 2018 can be found in Ross 2018; its supplement Ross 2019b covers most of 2019.

References

  1. ↑ Valdez-Mondragón, Alejandro; Juárez-Sánchez, Alma R. (2021-02-23). "A new epigean species of ricinuleid of the genus Pseudocellus (Arachnida: Ricinulei: Ricinoididae) from a tropical sub-deciduous forest in Oaxaca, Mexico". The Journal of Arachnology. 48 (3). doi:10.1636/JoA-S-20-014. ISSN   0161-8202. S2CID   232021020.
  2. ↑ Hans Jacob Hansen & William Sørensen (1904). On two orders of Arachnida. Cambridge University Press. pp.  1 182.
  3. ↑ Kay Pittard & Robert W. Mitchell (1972). "Comparative morphology of the life stages of Cryptocellus pelaezi (Arachnida, Ricinulei)". Graduate Studies. Texas Tech University. 1: 3–77.
  4. ↑ Gerald Legg (1976). "The external morphology of a new species of ricinuleid (Arachnida) from Sierra Leone". Journal of Zoology . 59 (1): 1–58. doi:10.1111/j.1096-3642.1976.tb01007.x.
  5. ↑ Gerald Legg (1976). "The external morphology of immature stages of Ricinoides karschi (Arachnida: Ricinulei)". Bulletin of the British Arachnological Society . 3: 243–248.
  6. ↑ L. van der Hammen (1979). "Comparative studies in Chelicerata I. The Cryptognomae (Ricinulei, Architarbi and Anactinotrichida)". Zoologische Verhandelingen . 174 (1): 1–62.
  7. 1 2 Niall Whalen, Paul Selden. "A new, giant ricinuleid (Arachnida, Ricinulei), from the Pennsylvanian of Illinois, and the identification of a new, ontogenetically stable, diagnostic character". Journal of Paleontology , Volume 95 , Issue 3 , May 2021 , pp. 601 - 612 DOI: https://doi.org/10.1017/jpa.2020.104
  8. ↑ J. H. Kennaugh (1968). "An examination of the cuticle of three species of Ricinulei (Arachnida)". Journal of Zoology . 156 (3): 393–404. doi:10.1111/j.1469-7998.1968.tb04361.x.
  9. ↑ G. Talarico, J. G. Palacios-Vargas & G. Alberti (2008). "Taste while chewing? Sensory structures in the chelicerae of Pseudocellus pearsei (Chamberlin & Ivie, 1938) (Ricinulei, Arachnida)". Revista Ibérica de Aracnología . 15: 47–53.
  10. ↑ G. Talarico, J. G. Palacios-Vargas & G. Alberti (2008). "The pedipalp of Pseudocellus pearsei (Ricinulei, Arachnida) – ultrastructure of a multifunctional organ". Arthropod Structure & Development . 37 (6): 511–521. doi:10.1016/j.asd.2008.02.001. PMID   18502688.
  11. ↑ Giovanni Talarico, Jose G. Palacios-Vargas, Mariano Fuentes Silva & Gerd Alberti (2005). "First ultrastructural observations on the tarsal pore organ of Pseudocellus pearsei and P. boneti (Arachnida, Ricinulei)". Journal of Arachnology . 33 (2): 604–612. doi:10.1636/04-110.1. JSTOR   4129861. S2CID   86221977.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  12. ↑ Giovanni Talarico, José G. Palacios-Vargas, Mariano Fuentes Silva & Gerd Alberti (2008). "Ultrastructure of tarsal sensilla and other integument structures of two Pseudocellus species (Ricinulei, Arachnida)". Journal of Morphology . 267 (4): 441–463. doi: 10.1002/jmor.10415 . PMID   16425267. S2CID   25580911.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  13. ↑ S. L. Tuxen (1974). "The African genus Ricinoides (Arachnida, Ricinulei)" (PDF). Journal of Arachnology . 1: 85–106.
  14. ↑ Jacques Millot (1945). "L'anatomie interne des Ricinulei". Annales des Sciences Naturelles, Zoologie (in French). 7: 1–29.
  15. ↑ Mario Ludwig; José G. Palacios-Vargas; Gerd Alberti (1994). "Cellular details of the midgut of Cryptocellus boneti (Arachnida: Ricinulei)". Journal of Morphology . 220 (3): 263–270. doi:10.1002/jmor.1052200305. PMID   29865385. S2CID   46930292.
  16. ↑ P. M. Brignoli (1973). "On some Ricinulei of Mexico with notes on the female genital apparatus (Arachnida, Ricinulei)". Accademia Nazionale dei Lincei. 171: 153–174.
  17. ↑ Gerd Alberti & José G. Palacios-Vargas (1984). "Fine structure of spermatogenesis and mature spermatozoa in Cryptocellus boneti Bolivar y Pieltain, 1941 (Arachnida, Ricinulei)". Journal of Ultrastructure Research . 87 (1): 1–12. doi:10.1016/S0022-5320(84)90111-4.
  18. ↑ G. Talarico, L. F. García Hernández & P. Michalik (2008). "The male genital system of the New World Ricinulei (Arachnida): ultrastructure of spermatozoa and spermiogenesis with special emphasis on its phylogenetic implications". Arthropod Structure & Development . 37 (5): 396–409. doi:10.1016/j.asd.2008.01.006. PMID   18539528.
  19. ↑ Ricinulei — Acari | SpringerLink
  20. ↑ Joachim Adis, Benjamin Messner & Norman Platnick (1999). "Morphological structures and vertical distribution in the soil indicate facultative plastron respiration in Cryptocellus adisi (Arachnida, Ricinulei) from Central Amazonia". Studies on Neotropical Fauna and Environment . 34 (1): 1–9. doi:10.1076/snfe.34.1.1.8915.
  21. ↑ Joachim U. Adis, Norman I. Platnick, José W. de Morais & José M. Gomes Rodrigues (1989). "On the abundance and ecology of Ricinulei (Arachnida) from Central Amazonia, Brazil". Journal of the New York Entomological Society . 97 (2): 133–140. JSTOR   25009750.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  22. ↑ J. A. L. Cooke (1967). "Observations on the biology of Ricinulei (Arachnida) with descriptions of two new species of Cryptocellus". Journal of Zoology . 151 (1): 31–42. doi:10.1111/j.1469-7998.1967.tb02864.x.
  23. ↑ Gerald Legg (1977). "Sperm transfer and mating in Ricinoides hanseni (Ricinulei: Arachnida)". Journal of Zoology . 182 (1): 51–61. doi:10.1111/j.1469-7998.1977.tb04140.x.
  24. ↑ García, L. F.; Torrado-León, E.; Talarico, G.; Peretti, A. V. (2015-07-01). "First Characterization of the Behavioral Repertory in a Ricinuleid: Cryptocellus narino Platnick & Paz 1979 (Arachnida, Ricinulei, Ricinoididae)". Journal of Insect Behavior. 28 (4): 447–459. doi:10.1007/s10905-015-9517-1. hdl: 11336/7938 . ISSN   1572-8889. S2CID   2409069.
  25. ↑ Whalen, Niall; Selden, Paul (May 2021). "A new, giant ricinuleid (Arachnida, Ricinulei), from the Pennsylvanian of Illinois, and the identification of a new, ontogenetically stable, diagnostic character". Journal of Paleontology. 95 (3): 601–612. doi:10.1017/jpa.2020.104. ISSN   0022-3360. S2CID   233301949.
  26. ↑ William Buckland (1837). Treatise IV. Geology and mineralogy with reference to natural theology. The Bridgewater treatises on the power, wisdom and goodness of God as manifested in the creation. (2nd ed.). London: William Pickering.
  27. ↑ P. A. Selden (1992). "Revision of the fossil ricinuleids". Transactions of the Royal Society of Edinburgh . Earth Sciences. 83 (4): 595–634. doi:10.1017/s0263593300003333. S2CID   85945454.
  28. ↑ Jörg Wunderlich (2012). "Description of the first fossil Ricinulei in amber from Burma (Myanmar), the first report of this arachnid order from the Mesozoic and from Asia, with notes on the related extinct order Trigonotarbida". In Jörg Wunderlich (ed.). Beiträge zur Araneologie, 7: Fifteen papers on extant and fossil spiders (Araneae). pp. 233–244.
  29. ↑ Jörg Wunderlich (2015). "New and rare fossil Arachnida in Cretaceous Burmese Amber (Amblypygi, Ricinulei and Uropygi: Thelephonida)". In Jörg Wunderlich (ed.). Beiträge zur Araneologie, 9: Mesozoic spiders and other fossil arachnids. pp. 409–436.
  30. ↑ Jörg Wunderlich (2017). "New extinct taxa of the arachnid order Ricinulei, based on new fossils preserved in mid Cretaceous Burmese amber". In Jörg Wunderlich (ed.). Beiträge zur Araneologie, 10. pp. 48–71.
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  35. 1 2 Gonzalo Giribet, Gregory D. Edgecombe, Ward C. Wheeler & Courtney Babbitt (2002). "Phylogeny and systematic position of Opiliones: a combined analysis of chelicerate relationships using morphological and molecular data" (PDF). Cladistics . 18 (1): 5–70. doi:10.1111/j.1096-0031.2002.tb00140.x. PMID   14552352. S2CID   16833833.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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  41. ↑ Lozano-Fernandez, L.; et al. (2019). "Increasing species sampling in chelicerate genomic-scale datasets provides support for monophyly of Acari and Arachnida". Nature Communications. 10 (2295): 459–462. Bibcode:2019NatCo..10.2295L. doi: 10.1038/s41467-019-10244-7 . PMC   6534568 . PMID   6534568.
  42. ↑ L. van der Hammen (1977). "A new classification of Chelicerata". Zoologische Mededelingen . 51 (20): 307–319.
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