For fossil groups and possible future splits, see text.
Neoptera is a major taxonomic group of insects that includes almost all the winged insects and specifically those considered to be related by the ability to fold their wings back over their abdomen. Traditionally, they are one of two major groups within the subclass Pterygota (the winged insects), the other being Paleoptera, which lack the ability to flex their wings in this manner.
Some groups within Neoptera do not have the ability to fold their wings back over their abdomen, such as various butterflies and moths, but this is considered to be a feature that was lost during evolutionary history (TOL 2003). This reflects the importance of lineage in modern classifications of organisms. With the advent of the theory of descent with modification, relatedness according to evolutionary lineage has been the primary consideration in classifying organisms. Likewise, the subclass Pterygota, which comprises the winged insects, also includes those species that do not have wings but in which it is assumed their ancestors did.
Insects, which are invertebrates comprising the Class Insecta, are the largest and (on land) most widely distributed taxon (taxonomic unit) within the Phylum Arthropoda. As arthropods, insects have jointed appendages, an exoskeleton (hard, external covering), segmented body, ventral nervous system, digestive system, open circulatory system, and specialized sensory receptors. Insects are distinguished from other arthropods by having three pairs of jointed legs; an abdomen that is divided into 11 segments and lacks any legs or wings; and a body separated into three parts (head, thorax, and abdomen), with one pair of antennae on the head. The true insects (that is, species classified in the Class Insecta) are also distinguished from all other arthropods in part by having ectognathous, or exposed, mouthparts.
Most species of insects, but by no means all, have wings as adults. Winged insects are placed in the Subclass Pterygota. (Wingless insects, such as the silverfishes and bristletails, are placed in the subclass Apterygota.) Pterygota also includes some insect groups that are "secondarily wingless"; that is, it is considered that the ancestors of these insects had wings but were lost through the process of descent with modification.
Neoptera are those members of Pterygota that are able to fold their wings back over their abdomen, as a result of special structures at the base of their wings (TOL 2003). A key component of this folding mechanism is the pleural wing-folding muscle and the third axillary sclerite (TOL 2003). Neoptera generally is considered an "infraclass." Those insects that are not able to fold their wings in this manner—such as the mayflies and the order Odonata (dragonflies, damselflies), are placed in the infraclass Paleoptera. Some insects placed in Neoptera are not able to fold their wings back but this is considered to have been a feature that their ancestors had and was lost.
The Neoptera may be subdivided in various ways. The Integrated Taxonomic Information System (ITIS) lumps all neopteran orders together in this infraclass without subdivision. Other authorities recognize several superorders within it.
Almost universally accepted as two major divisions of Neoptera are the Exopterygota and the Endopterygota. The Exopterygota are hemimetabolous neopterans (incomplete metamorphosis) in which the wing buds are already externally visible before the adult stage and in which no pupa or chrysalis stage occurs. The Endopterygota are holometabolous insects (complete metamorphosis, with distinctive larval, pupal, and adult stages) in which the wings develop inside the body during the larval stage and only become external appendages during the pupa or chrysalis stage. Endopterygota literally means "internal winged forms" while Exopterygota means "external winged forms," indicating whether the wing buds are evident externally in the later immature stages (in instars before the penultimate) or whether the future wing tissues are entirely internalized and make their first appearance in the penultimate (pupal) stage (TOL 1995).
Although members of Exopterygota, such as true bugs, develop wings on the outside of their bodies without going through a true pupal stage, a few have something resembling a pupa (e.g., Aleyrodidae).
Neoptera also may be subdivided into the Endopterygota (insects with complete metamorphosis, such as beetles, flies, wasps, and butterflies), the Hemipteroid Assemblage (bugs, lice, and thrips), and the "lower Neoptera" (the many other living orders, such as Plecoptera or stoneflies, Orthoptera including grasshoppers, and Dictyoptera, including mantids and cockroaches). Another name for Endoterygota is Holometabola, indicating that these species go through complete metamorphosis.
As of recently, there are several attempts to resolve the neopteran diversity further. While this appears to be less controversial than in the (apparently paraphyletic) "Palaeoptera," there are nonetheless lots of unresolved questions. For example, the hymenopterans, traditionally considered highly advanced due to their intricate social systems, seem to be far more basal among the Endopterygota, as suggested by their relatively plesiomorphic anatomy and molecular data. The exact position of the proposed Dictyoptera is also uncertain, namely whether they are better considered Exopterygota or basal neopterans.
Here is one particularly classification of living and fossil neopteran orders, as well as some proposed superorders. Note that a number of taxonomies exist, including Dictyoptera as an order, with Blattodea, Isoptera, and Mantodea as suborders of Dictyoptera.
Proposed superorder Dictyoptera
Proposed superorder Paraneoptera
Proposed superorder Mecopteroidea/Antliophora
Proposed superorder Amphiesmenoptera
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