Tetrapulmonata is a non-ranked supra-ordinal clade of

arachnids 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 vine ...

. It is composed of the

extant Extant is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Extant taxon, a taxon which is not extinct, ...

orders

Thelyphonida Thelyphonida is an arachnid order comprising invertebrates commonly known as whip scorpions or vinegaroons (also spelled vinegarroons and vinegarones). They are often called uropygids in the scientific community based on an alternative name for ...

(whip scorpions), Schizomida (short-tailed whip scorpions),

Amblypygi Amblypygi is an ancient order of arachnid chelicerate arthropods also known as African cave-dwelling spiders, whip spiders and tailless whip scorpions (not to be confused with whip scorpions or vinegaroons that belong to the related order Thelypho ...

(tail-less whip scorpions) and

Araneae Spiders (order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species dive ...

(spiders). It is the only supra-ordinal group of arachnids that is strongly supported in

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

studies. Two extinct orders are also placed in this clade,

Haptopoda ''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 ...

and

Uraraneida Uraraneida is an extinct order of arachnids, known from fossils of Middle Devonian, Permian and possibly Cretaceous age. Two genera of fossils have been definitively placed in this order: ''Attercopus'' from the Devonian of United States and ''P ...

. In 2016, a newly described fossil arachnid, '' Idmonarachne'', was also included in the Tetrapulmonata; it has not been assigned to an order.

Etymology

It receives its name from the presence of paired

book lung 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 con ...

s occupying the second and third opisthosomal segments, although the posterior pair is absent in Schizomida and most

araneomorph The Araneomorphae (also called the Labidognatha) are an infraorder of spiders. They are distinguishable by chelicerae (fangs) that point diagonally forward and cross in a pinching action, in contrast to the Mygalomorphae (tarantulas and their cl ...

spiders. Previous

synonym A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are al ...

s of this lineage are rejected; "Caulogastra Pocock, 1893" refers to pedicel, which is symplesiomorphic for the lineage and convergent with

Solifugae 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 ne ...

, and "Arachnidea Van der Hammen, 1977" is easily confused with

Arachnid 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 ...

a. The clade is referred to as Pantetrapulmonata when the extinct trigonotarbid arachnids are included. The name "Pulmonata" has been used for this group as recently as 2000, in the first paragraph of an article in

Journal of Paleontology The ''Journal of Paleontology'' is a peer-reviewed scientific journal covering the field of paleontology. It is published by the Paleontological Society. Indexing The ''Journal of Paleontology'' is indexed in: *BIOSIS Previews *Science Citatio ...

, but this creates an

ambiguity Ambiguity is the type of meaning in which a phrase, statement or resolution is not explicitly defined, making several interpretations plausible. A common aspect of ambiguity is uncertainty. It is thus an attribute of any idea or statement w ...

because

Pulmonata Pulmonata or pulmonates, is an informal group (previously an order, and before that a subclass) of snails and slugs characterized by the ability to breathe air, by virtue of having a pallial lung instead of a gill, or gills. The group include ...

is a group of gastropods.

Characteristics

In addition to the two pairs of book lungs, other

synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to hav ...

of Tetrapulmonata include a large postcerebral pharynx (reduced in Uropygi), prosomal endosternite with four segmental components, subchelate chelicerae, a complex coxotrochanteral joint in the walking legs, a pretarsal depressor muscle arising in the patella (convergent with Dromopoda, lost in Amblypygi), a pedicel formed, in part, by ventral elements of the second opisthomal segment and a

spermatozoon A spermatozoon (; also spelled spermatozoön; ; ) is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote. (A zygote is a single cell, with a complete set of chromosom ...

axoneme with a 9+3 microtubule arrangement.

Phylogeny

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

published in 2014 divides the Tetrapulmonata into two clades, the Schizotarsata and the Serikodiastida. The Schizotarsata have walking legs II–IV with the tarsus having a specific pattern of three subsegments (tarsomeres). The Serikodiastida (

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

for "silk workers") share the ability to produce and use silk. The sister clade to Tetrapulmonata is the extinct order

Trigonotarbida The order Trigonotarbida is a group of extinct arachnids whose fossil record extends from the late Silurian to the early Permian (Pridoli to Sakmarian).Dunlop, J. A., Penney, D. & Jekel, D. 2020A summary list of fossil spiders and their relatives ...

; together they form a clade that has been called "Pantetrapulmonata". In 2016, a fossil arachnid from the

Late Carboniferous Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effe ...

(

Pennsylvanian Pennsylvanian may refer to: * A person or thing from Pennsylvania * Pennsylvanian (geology) The Pennsylvanian ( , also known as Upper Carboniferous or Late Carboniferous) is, in the International Commission on Stratigraphy, ICS geologic timesca ...

) age was described in the genus '' Idmonarachne''. Based on its overall morphology, it was considered to belong to the Serikodiastida, although the presence of silk-producing spigots was not demonstrated. Like uraraneids, it lacked spinnerets, but it also lacked a flagellum, thus resembling spiders. A cladogram based on morphology placed ''Idmonarachne'' between uraraneids and spiders: The Late Carboniferous appears to be a time when there was a greater diversity of tetrapulmonate arachnids.

References

Sources

Jeffrey W. Shultz. 2007. "A phylogenetic analysis of the arachnid orders based on morphological characters". ''Zoological Journal of the Linnean Society'' 150(?):221-265. (See ''External links'' below).

External links

Shultz on arachnid morphology
At
Index of /mndi/Aracnologia
At
Museu Nacional / UFRJ / Departamento de Invertebrados
At
Museu Nacional / UFRJ
{{Taxonbar, from=Q3821682 Arachnid taxonomy Paleozoic arachnids Mesozoic arachnids Cenozoic arachnids Extant Pennsylvanian first appearances