Odonata is an order of flying insects that includes the dragonflies and damselflies.
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.
Neoptera is a classification group that includes most orders of the winged insects, specifically those that can flex their wings over their abdomens. This is in contrast with the more basal orders of winged insects, which are unable to flex their wings in this way.
Holometabola, also known as Endopterygota, is a superorder of insects within the infraclass Neoptera that go through distinctive larval, pupal, and adult stages. They undergo a radical metamorphosis, with the larval and adult stages differing considerably in their structure and behaviour. This is called holometabolism, or complete metamorphism.
The Exopterygota, also known as Hemimetabola, are a superorder of insects of the subclass Pterygota in the infraclass Neoptera, in which the young resemble adults but have externally developing wings. They undergo a modest change between immature and adult, without going through a pupal stage. The nymphs develop gradually into adults through a process of moulting.
The name Apterygota is sometimes applied to a former 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 group Apterygota is not a clade; it is paraphyletic, and not recognized in modern classification schemes. As defined, the group contains two separate clades of wingless insects: Archaeognatha 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, while Archaeognatha is sister to this lineage.
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 in strata from the remainder of the Paleozoic Era and more recent periods. For historical reasons an alternative name for the order is Microcoryphia.
The most recent understanding of the evolution of insects is based on studies of the following branches of science: molecular biology, insect morphology, paleontology, insect taxonomy, evolution, embryology, bioinformatics and scientific computing. It is estimated that the class of insects originated on Earth about 480 million years ago, in the Ordovician, at about the same time terrestrial plants appeared. Insects are thought to have evolved from a group of crustaceans. The first insects were landbound, but about 400 million years ago in the Devonian period one lineage of insects evolved flight, the first animals to do so. The oldest insect fossil has been proposed to be Rhyniognatha hirsti, estimated to be 400 million years old, but the insect identity of the fossil has been contested. Global climate conditions changed several times during the history of Earth, and along with it the diversity of insects. The Pterygotes underwent a major radiation in the Carboniferous while the Endopterygota underwent another major radiation in the Permian.
The name Palaeoptera has been traditionally applied to those ancestral groups of winged insects that lacked the ability to fold the wings back over the abdomen as characterizes the Neoptera. The Diaphanopterodea, which are palaeopteran insects, had independently and uniquely evolved a different wing-folding mechanism. Both mayflies and dragonflies lack any of the smell centers in their brain found in Neoptera.
Zygentoma are an order in the class Insecta, and consist of about 550 known species. The Zygentoma include the so-called silverfish or fishmoths, and the firebrats. A conspicuous feature of the order are the 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, although the cerci of Zygentoma, unlike in the latter order, are nearly as long as the epiproct.
Protacanthopterygii is a ray-finned fish taxon ranked as a superorder of the infraclass Teleostei. They inhabit both marine and freshwater habitats. They appear to have evolved in the Cretaceous or perhaps late Jurassic, originating probably roughly 150 million years ago; fossils of them and the closely related Otocephala are known from throughout the Cretaceous.
The Odonatoptera are a superorder of ancient winged insects, placed in the probably paraphyletic group Palaeoptera. The dragonflies and damselflies are the only living members of this group, which was far more diverse in the late Paleozoic and contained gigantic species, including the griffinflies of the order Meganisoptera. This lineage dates back at least to the Bashkirian, not quite 320 million years ago.
There are various disparate groups of wingless insects. Apterygota are a subclass of small, agile insects, distinguished from other insects by their lack of wings in the present and in their evolutionary history. They include Thysanura . Some species lacking wings are members of insect orders that generally do have wings. Some do not grow wings at all, having "lost" the possibility in the remote past. Some have reduced wings that are not useful for flying. Some develop wings but shed them after they are no longer useful. Other groups of insects may have castes with wings and castes without, such as ants. Ants have alate queens and males during the mating season and wingless workers, which allows for smaller workers and more populous colonies than comparable winged wasp species.
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 a hypothetical ancestral mandible with a single ball joint (monocondyl); the members of Archaeognatha do in fact have dicondylic mandibles, though they are not identical to the structure seen in "true" dicondylic insects.
Metapterygota is a clade of winged insects containing order Odonata and Infraclass Neoptera. They share morphological characteristics of a loss of caudal filaments and a subimago stage. Genetically the clade is supported by similarities in the mitochondrial genomes.
Panorpida or Mecopterida is a proposed superorder of Holometabola. The conjectured monophyly of the Panorpida is historically based on morphological evidence, namely the reduction or loss of the ovipositor and several internal characteristics, including a muscle connecting a pleuron and the first axillary sclerite at the base of the wing, various features of the larval maxilla and labium, and basal fusion of CuP and A1 veins in the hind wings. The monophyly of the Panorpida is supported by recent molecular data.
Tricholepidion is a genus of wingless insect belonging to Zygentoma, with only a single described species T. gertschi, native to the northern coast of California in Western North America. It lives under dead bark and in rotting wood of conifers in mesophytic forests. It is alternatively considered the only living member of the family Lepidotrichidae, which also includes Lepidotrix from Eocene aged European amber, or the only member of the family Tricholepidiidae. The taxonomic position of Tricholepidion is uncertain, in some molecular phylogenetics studies it has been recovered as less closely related to flying insects (Pterygota) than the rest of Zygentoma is, rendering Zygentoma paraphyletic. Each compound eye contains ~40 ommatidia, and they have three ocelli. Scales on the body are absent. Unlike Archaeognatha and the other families of Zygentoma, which have three- and sometimes two-segmented tarsi, they have five-segmented tarsi like many winged insects.
The cohort Polyneoptera is a proposed taxonomic ranking for the Orthoptera and all other neopteran insects believed to be more closely related to Orthoptera than to any other insect orders. They were formerly grouped together with the Palaeoptera and Paraneoptera as the Hemimetabola or Exopterygota on the grounds that they have no metamorphosis, the wings gradually developing externally throughout the nymphal stages.
Hymenopterida is a superorder of holometabolous (metamorphosing) insects. As originally circumscribed, it included Hymenoptera and the orders in Panorpida. However, more recent studies find Hympenoptera as sister to the other members of Holometabola and the superorder is restricted to Hymenoptera.
