The Archaeognatha are an order of apterygotes, known by various common names such as jumping bristletails. Among extant insect taxa they are some of the most evolutionarily primitive; they appeared in the Middle Devonian period at about the same time as the arachnids. Specimens that closely resemble extant species have been found as both body and trace fossils (the latter including body imprints and trackways) in strata from the remainder of the Paleozoic Era and more recent periods. For historical reasons an alternative name for the order is Microcoryphia.
Until the late 20th century the suborders Zygentoma and Archaeognatha comprised the order Thysanura; both orders possess three-pronged tails comprising two lateral cerci and a medial epiproct or appendix dorsalis. Of the three organs, the appendix dorsalis is considerably longer than the two cerci; in this the Archaeognatha differ from the Zygentoma, in which the three organs are subequal in length. In the late 20th century, it was recognized that the order Thysanura was paraphyletic, thus the two suborders were each raised to the status of an independent monophyletic order, with Archaeognatha sister taxon to the Dicondylia, including the Zygentoma.
Temporal range: Devonian–Recent:320
Archaeognatha are small insects with elongated bodies and backs that are arched, especially over the thorax. They have three long tail-like structures, of which the lateral two are cerci, while the medial filament, which is longest, is an epiproct. The antennae are flexible. The two large compound eyes meet at the top of the head, and there are three ocelli. The mouthparts are partly retractable, with simple chewing mandibles and long maxillary palps.:341–343
Archaeognatha differ from Zygentoma in various ways, such as their relatively small head, their bodies being compressed laterally (from side to side) instead of flattened dorsiventrally, and in their being able to use their tails to spring up to 30 cm (12 in) into the air if disturbed. They also are unique among insects in possessing small, articulated "styli" on the hind (and sometimes middle) coxae and on sternites 2 to 9, which some authorities consider to be vestigial appendages. They have paired eversible membranous vesicles through which they absorb water.
Further unusual features are that the abdominal sternites are each composed of three sclerites, and they cement themselves to the substrate before molting. As in the Zygentoma, the body is covered with readily detached scales, that make the animals difficult to grip and also may protect the exoskeleton from abrasion. The thin exoskeleton offers little protection against dehydration. The animals accordingly must remain in moist air, such as in cool, damp situations under stones or bark.
The name Archaeognatha is derived from Greek, ἀρχαῖος, (archaios) meaning ancient and γνάθος (gnathos) meaning "jaw". This refers to the articulation of the mandibles, which have a single phylogenetically primitive condyle each, where all more derived insects have two.
|Families||No. of Species||Defining Notes||Image|
|Machilidae||250||Most are restricted to rocky shorelines||Need specific image|
|Meinertellidae||20||Lack scales at base of hind legs and antennae||Need specific image|
Archaeognatha occur in a wide range of habitats. While most species live in moist soil, others have adapted to chaparral, and even sandy deserts. They feed primarily on algae, but also lichens, mosses, or decaying organic detritus.
During courtship, the males spin a thread from the abdomen, attach one end to the substrate, and string packages of sperm (spermatophores) along it. After a series of courtship dances, the female picks up the spermatophores and places them on her ovipositor. She then lays a batch of around 30 eggs in a suitable crevice. The young resemble the adults, and take up to two years to reach sexual maturity, depending on the species and conditions such as temperature and available food.
Unlike most insects, the adults continue to moult after reaching adulthood, and typically mate once at each instar. Archaeognaths may have a total lifespan of up to four years, longer than most larger insects.
Afrochilis insularis is the only known member of the genus Afrochilis of the family Machilidae, which is from the order Archaeognatha. It is endemic to the Socotra archipelago, a group of isolated islands.Afromachilis makungu
Afromachilis makungu is the only known member of the genus Afromachilis of the family Machilidae, which is from the order Archaeognatha. It is found in Katanga, a province of the Democratic Republic of the Congo. It has one synonym, Paramachilis makungu Wygodzinsky, 1952Allopsontus
Allopsontus is a genus of the family Machilidae which belongs to the insect order Archaeognatha (jumping bristletails). Certain species in this genus have been found as high as 5 kilometres above sea level on the Himalayas.Apterygota
The name Apterygota is sometimes applied to a subclass of small, agile insects, distinguished from other insects by their lack of wings in the present and in their evolutionary history; notable examples are the silverfish, the firebrat, and the jumping bristletails. Their first known occurrence in the fossil record is during the Devonian period, 417–354 million years ago.
The nymphs (younger stages) go through little or even no metamorphosis, hence they resemble the adult specimens. Their skin is thin, making them appear translucent.
Currently, no species are listed as being at conservation risk.
The term Apterygota refers to two separate clades of wingless insects: Archeognatha comprises jumping bristletails, while Zygentoma comprises silverfish and firebrats. The Zygentoma are in the clade Dicondylia with winged insects, a clade that includes all other insects. The group Apterygota is not a clade; it is paraphyletic.Catamachilis
Catamachilis is a genus of the family Machilidae which belongs to the insect order Archaeognatha (jumping bristletails). They mostly occur in Spain.Charimachilis
Charimachilis is a genus of the family Machilidae which belongs to the insect order Archaeognatha (jumping bristletails). They are found in southern and eastern Europe.Dicondylia
The Dicondylia are a taxonomic group (taxon) that includes all insects except the jumping bristletails (Archaeognatha). Dicondylia have a mandible attached with two hinges to the head capsule (dicondyl), in contrast to the original mandible with a single ball joint (monocondyl).Dilta
Dilta is a genus of primitive insects belonging to the family Machilidae. These insects are slender and wingless with dull, often mottled, colouring. They are typically found on the ground in heavily vegetated places. Dilta spp are restricted to western Europe and parts of north Africa.Eumetabola
Eumetabola is an unranked category of Neoptera. Two large unities known as the Paurometabola and Eumetabola are probably from the adelphotaxa of the Neoptera after exclusion of the Plecoptera. The monophyly of these unities appears to be weakly justified.Holoptic
Holoptic refers to one of the ways in which the Arthropod eye develops, particularly the eyes of various species of insects. As opposed to dichoptic and cycloptic eyes, holoptic eyes meet along the median dorsal line of the head, in many species nearly covering the exterior of the head. Holoptic eyes are typical of several Dipteran males, in particular some Syrphidae, Tabanidae, Pipunculidae, and Acroceridae. Some other insect orders that include species with holoptic males and some in which the females are holoptic as well, include the Coleoptera, Anisoptera and Archaeognatha.Machilidae
The Machilidae are a family of insects belonging to the order Archaeognatha (the bristletails). There are around 250 described species worldwide. These insects are wingless, elongated and more or less cylindrical with a distinctive humped thorax and covered with tiny, close-fitting scales. The colour is usually grey or brown, sometimes intricately patterned. There are three "tails" at the rear of the abdomen: two cerci and a long central epiproct. They have large compound eyes, often meeting at a central point. They resemble the silverfish and the firebrat, which are from a different order, Zygentoma.
Machilids undergo virtually no metamorphosis during their life cycles, and both nymphs and adults are generally inconspicuous herbivores and scavengers. Many species are restricted to rocky shorelines, but some are found in well-vegetated habitats inland. They can move very fast and often escape by jumping considerable distances when disturbed.
Like all Archaeognatha, machilids transfer sperm indirectly from male to female. Some species can spin silken threads that lead the female to the spermatophore. Other species can produce silken stalks on which they place droplets of sperm.Meinertellidae
The Meinertellidae are a small family of basal insects belonging to the order Archaeognatha. They are sometimes known as rock bristletails. These insects can be distinguished from members of the other Archaeognatha family, Machilidae, by the lack of scales at the base of the legs and antennae.Metapterygota
Metapterygota is a clade of winged insects containing order Odonata and Infraclass Neoptera.Metasoma
The metasoma is the posterior part of the body, or tagma, of arthropods whose body is composed of three parts, the other two being the prosoma and the mesosoma. In insects, it contains most of the digestive tract, respiratory system, and circulatory system, and the apical segments are typically modified to form genitalia. In a few of the most primitive insects (the Archaeognatha), the metasomal segments bear small, articulated appendages called "styli", which are often considered to be vestigial. There are also pre-apical appendages in most insect orders, called cerci, which may be multi-segmented and almost resembling a posterior pair of antennae; these may be variously modified, or lost entirely. Otherwise, most adult insects lack appendages on the metasoma, though many larval insects (e.g., caterpillars) have some form of appendages, such as prolegs or, in aquatic insects, gills.
In apocritan Hymenoptera (wasps, bees and ants), the metasoma consists of the second abdominal segment (which typically forms a petiole) and those segments posterior to it, and is often called the gaster rather than referring to it as the "abdomen"; in these insects, the first abdominal segment is called the propodeum and is fused to the thorax. The metasoma is armoured with chitinous plates on the upper surface by the tergites and on the lower surface by the sternites.In scorpions, the metasoma is the tail. In other chelicerates, such as spiders, the mesosoma is fused with the metasoma to form the opisthosoma.Petrobius
Petrobius is a genus of jumping bristletails (family Machilidae). Many of these primitive insects are restricted to rocky shorelines.Petrobius maritimus
Petrobius maritimus, the shore bristletail or sea bristletail, is a species of Archaeognatha found on rocky shores from the Mediterranean Sea to the North Sea .Individuals may grow up to 15 mm and are grey in colour, with long bristly antennae and a triple forked tail .Pterygota
The Pterygota are a subclass of insects that includes the winged insects. It also includes insect orders that are secondarily wingless (that is, insect groups whose ancestors once had wings but that have lost them as a result of subsequent evolution).The pterygotan group comprises almost all insects. The insect orders not included are the Archaeognatha (jumping bristletails) and the Zygentoma (silverfishes and firebrats), two primitively wingless insect orders. Also not included are the three orders no longer considered to be insects: Protura, Collembola, and Diplura.Thysanura
Thysanura is the now deprecated name of what was, for over a century, recognised as an order in the class Insecta. The two constituent groups within the former order, the Archaeognatha and the Zygentoma, share several characteristics, such as of having three long caudal filaments, the lateral ones being the cerci, while the one between (telson) is a medial cerciform appendage, specifically an epiproct. They are also both wingless, and have bodies covered with fine scales, rather like the scales of the practically unrelated Lepidoptera. In the late 20th century, it was recognized that the two suborders were not sister taxa, therefore Thysanura was paraphyletic, and the two suborders were each raised to the status of an independent monophyletic order, with Archaeognatha sister taxon to the Dicondylia, including the Zygentoma.
Although the group Thysanura is no longer recognized, the name still appears in some published material. Another name used to separate the two groups from winged insects is Apterygota.Zygentoma
Zygentoma are an order in the class Insecta, and consist of about 400 known species. The Zygentoma include the so-called silverfish or fishmoths, and the firebrats. A conspicuous feature of the order is that the members all have three long caudal filaments. The two lateral filaments are cerci, and the medial one is an epiproct or appendix dorsalis. In this they resemble the Archaeognatha, though, unlike in the latter order, the cerci of Zygentoma are nearly as long as the epiproct.Until the late twentieth century the Zygentoma were regarded as a suborder of the Thysanura, until it was recognized that the order Thysanura was paraphyletic, thus the two suborders were each raised to the status of an independent monophyletic order, with Archaeognatha sister taxon to the Dicondylia, including the Zygentoma.
Extant Archaeognatha families