Tetrapulmonata is a non-ranked supra-ordinal

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

arachnid Arachnids are arthropods in the Class (biology), class Arachnida () of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, opiliones, harvestmen, Solifugae, camel spiders, Amblypygi, wh ...

s. It is composed of the

extant Extant or Least-concern species, least concern 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 * Exta ...

orders

Uropygi Uropygi is an arachnid order comprising invertebrates commonly known as whip scorpions or vinegaroons (also spelled vinegarroons and vinegarones). They are often called uropygids. The name "whip scorpion" refers to their resemblance to scorpion ...

(whip scorpions),

Schizomida Schizomida, also known as sprickets or short-tailed whip-scorpions, is an order of arachnids, generally less than in length. The order is not yet widely studied. E. O. Wilson has identified schizomids as among the "groups of organisms that des ...

(short-tailed whip scorpions),

Amblypygi Amblypygi is an order of arachnids also known as whip-spiders or tailless whip-scorpions, not to be confused with whip-scorpions or vinegaroons that belong to the related order Thelyphonida. The name "amblypygid" means "blunt tail", a referen ...

(tail-less whip scorpions) and Araneae (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 and

Uraraneida Uraraneida is an extinct order of Paleozoic arachnids related to modern Spider, spiders. Two genera of fossils have been definitively placed in this order: ''Attercopus'' from the Devonian of United States and ''Permarachne'' from the Permian of ...

. 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 A name is a term used for identification by an external observer. They can identify a class or category of things, or a single thing, either uniquely, or within a given context. The entity identified by a name is called its referent. A person ...

from the presence of paired book lungs occupying the second and third opisthosomal segments, although the posterior pair is absent in Schizomida and most araneomorph spiders. Previous

synonym A synonym is a word, morpheme, or phrase that means precisely 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 a ...

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 (biology), order of Arachnid, arachnids known variously as solifuges, sun spiders, camel spiders, and wind scorpions. The order includes more than 1,000 described species in about 147 genus, genera. Despite the common names, ...

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

Arachnid Arachnids are arthropods in the Class (biology), class Arachnida () of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, opiliones, harvestmen, Solifugae, camel spiders, Amblypygi, wh ...

a. The clade is referred to as Pantetrapulmonata when the extinct

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

arachnids are included. The name "Pulmonata" has been used for this

group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...

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 managed and published by Cambridge University Press on behalf of the Paleontological Society. Indexing The ''Journal of Paleontology ...

, but this creates

ambiguity Ambiguity is the type of meaning (linguistics), meaning in which a phrase, statement, or resolution is not explicitly defined, making for several interpretations; others describe it as a concept or statement that has no real reference. A com ...

because Pulmonata is a group of

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

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 ...

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; : spermatozoa; ) is a motile sperm cell (biology), cell produced by male animals relying on internal fertilization. A spermatozoon is a moving form of the ploidy, haploid cell (biology), cell that is ...

axoneme with a 9+3

microtubule Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nanometer, nm and have an inner diameter bet ...

arrangement.

Phylogeny

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

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: 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 of all kno ...

for "silk workers") share the ability to produce and use silk. The sister clade to Tetrapulmonata is the extinct order Trigonotarbida; together they form a clade that has been called "Pantetrapulmonata", to which the Carboniferous genus '' Douglassarachne'' was also referred in 2024. In 2016, a fossil arachnid from the

Late Carboniferous Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * Late (The 77s album), ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudo ...

( Pennsylvanian) 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