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      • 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 nymphs (younger stages) go through little or even no metamorphosis, hence they resemble the adult specimens (ametabolism).
      Currently, no species are listed as being at conservation risk.


      Characteristics


      The primary characteristic of the apterygotes is they are primitively wingless. While some other insects, such as fleas, also lack wings, they nonetheless descended from winged insects but have lost them during the course of evolution. By contrast, the apterygotes are a primitive group of insects that diverged from other ancient orders before wings evolved.
      Apterygotes, however, have the demonstrated capacity for directed, aerial gliding descent from heights. It has been suggested by researchers that this evolved gliding mechanism in apterygotes might have provided an evolutionary basis from which winged insects would later evolve the capability for powered flight.
      Apterygotes also have a number of other primitive features not shared with other insects. Males deposit sperm packages, or spermatophores, rather than fertilizing the female internally. When hatched, the young closely resemble adults and do not undergo any significant metamorphosis, and lack even an identifiable nymphal stage. They continue to molt throughout life, undergoing multiple instars after reaching sexual maturity, whereas all other insects undergo only a single instar when sexually mature.
      Apterygotes possess small unsegmented appendages, referred to as "styli", on some of their abdominal segments, but play no part in locomotion. They also have long, paired abdominal cerci and a single median, tail-like caudal filament, or telson.
      While all members of winged insects (Pterygota) has a closed amniotic cavity during embryonic development, this varies within Apterygota. In Archaeognatha, species like Petrobius brevistylis and Pedetontus unimaculatus have a wide open cavity, whereas Trigoniophthalmus alternatus does not have an amniotic cavity at all. In Zygentoma, the cavity is open through a narrow canal called the amniopore in the species Thermobia domestica and Lepisma saccharina, but in other species like Ctenolepisma lineata it is completely closed.


      History of the concept


      The composition and classification of Apterygota changed over time. By the mid-20th century, the subclass included four orders (Collembola, Protura, Diplura, and Thysanura). With the advent of a more rigorous cladistic methodology, the subclass was proven paraphyletic. While the first three groups formed a monophyletic group, the Entognatha, distinguished by having mouthparts submerged in a pocket formed by the lateral and ventral parts of the head capsule, the Thysanura (Zygentoma plus Archaeognatha) appeared to be more closely related to winged insects. The most notable synapomorphy proving the monophyly of Thysanura+Pterygota is the absence of intrinsic antennal muscles, which connect the antennomeres in entognaths, myriapods, and crustaceans. For this reason, the whole group is often termed the Amyocerata, meaning "lacking antennal muscles".
      However, the Zygentoma are now considered more closely related to the Pterygota than to the Archaeognatha, thus rendering even the amyocerate apterygotes paraphyletic, and resulting in the dissolution of Thysanura into two separate monophyletic orders.


      References



      Firefly Encyclopedia of Insects and Spiders, edited by Christopher O'Toole, ISBN 1-55297-612-2, 2002

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    Apterygota - Wikipedia

    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.

    Insect Classification - Subclass Apterygota - ThoughtCo

    17 Mar 2017 · What are apterygotes? Learn which arthropods are classified as Apterygota, and what that means.

    Definition, Behavior, Evolution, & Classification - Britannica

    apterygote, broadly, any of the primitive wingless insects, distinct from the pterygotes, or winged insects.

    Apterygota – ENT 425 – General Entomology - North Carolina …

    They are strikingly similar to insects that we recognize today as bristletails. These “most primitive” of all insects are members of the subclass apterygota (from the Greek “ a- ” meaning without and “ pterygo ” meaning wing). They are completely wingless and have ametabolous development.

    Apterygota - Simple English Wikipedia, the free encyclopedia

    The Apterygota are a small subclass of primitive insects . They are insects which have never had wings at any time in their evolutionary history. Their first known occurrence in the fossil record is in the Rhynie chert of the Devonian period, ~400 million years ago.

    Apterygota - Encyclopedia.com

    23 Mei 2018 · Apterygota A subclass of small primitive wingless insects in which metamorphosis is slight or absent. It includes the orders Thysanura and Diplura (bristletails), Collembola (springtails), and Protura. Compare Pterygota. See Hexapoda.

    apterous, apterygote, apterygota - BugGuide.Net

    05 Agu 2010 · Apterygota refers to the orders of insects (apterogytes) that lack wings at all stages (also called ametabola). This includes:

    Apterygota - Royal Entomological Society

    The Apterygota, which formerly included the other primitively wingless insects currently placed in the class Entognatha, are now restricted to the two orders Archaeognatha and Zygentoma, which in turn were formerly united as the Thysanura.

    Apterygote - Insects, Arthropods, Hexapods | Britannica

    Apterygotes differ from pterygotes in lacking wings and undergoing simple metamorphosis. They differ also in the structure of the thorax and in the development of abdominal appendages.

    Apterygote - Microhabitats, Adaptations, Reproduction | Britannica

    Most apterygotes live in soil and leaf litter or are associated with plants and rotting logs in moist regions. Collembolans are also found in aquatic environments, caves, permanent ice fields and snow, and insect and animal nests. Moisture is an important ecological factor in habitat selection.