The nameApterygotais sometimes applied to a formersubclassof small, agileinsects,distinguished from other insects by their lack of wings in the present and in their evolutionary history; notable examples are thesilverfish,thefirebrat,and thejumping bristletails.Their first known occurrence in the fossil record is during theDevonianperiod, 417–354 million years ago. The group Apterygota is not a clade; it isparaphyletic,and not recognized in modern classification schemes. As defined, the group contains two separatecladesof wingless insects:Archaeognathacomprises jumping bristletails, whileZygentomacomprises silverfish and firebrats. The Zygentoma are in the cladeDicondyliawith winged insects, a clade that includes all other insects, while Archaeognatha is sister to this lineage.[4]
| Apterygota Temporal range:[1]
| |
|---|---|
| |
| Petrobius maritimus(Archaeognatha:Machilidae) | |
Scientific classification
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Subclass: | Apterygota Brauer 1885[2] |
| Groups included | |
| Cladisticallyincluded but traditionally excluded taxa | |
Thenymphs(younger stages) go through little or even nometamorphosis,hence they resemble the adult specimens (ametabolism). Currently, nospeciesare listed as being at conservation risk.
Characteristics
editThe primary characteristic of the apterygotes is they are primitively wingless. While some other insects, such asfleas,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.[5]
Apterygotes also have a number of other primitive features not shared with other insects. Males deposit sperm packages, orspermatophores,rather than fertilizing the femaleinternally.When hatched, the young closely resemble adults and do not undergo any significantmetamorphosis,and lack even an identifiablenymphalstage. They continue to molt throughout life, undergoing multipleinstarsafter 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 theirabdominalsegments, but play no part in locomotion. They also have long, paired abdominalcerciand a single median, tail-like caudal filament, or telson.[6]
While all members of winged insects (Pterygota) has a closed amniotic cavity during embryonic development, this varies within Apterygota. In Archaeognatha, species likePetrobius brevistylisandPedetontus unimaculatushave a wide open cavity, whereasTrigoniophthalmus alternatusdoes not have an amniotic cavity at all. In Zygentoma, the cavity is open through a narrow canal called the amniopore in the speciesThermobia domesticaandLepisma saccharina,but in other species likeCtenolepisma lineatait is completely closed.[7]
History of the concept
editThe composition and classification of Apterygota changed over time. By the mid-20th century, the subclass included four orders (Collembola,Protura,Diplura,andThysanura). With the advent of a more rigorouscladisticmethodology, the subclass was provenparaphyletic.While the first three groups formed a monophyletic group, theEntognatha,distinguished by having mouthparts submerged in a pocket formed by the lateral and ventral parts of the head capsule, the Thysanura (ZygentomaplusArchaeognatha) appeared to be more closely related towinged insects.The most notablesynapomorphyproving themonophylyof Thysanura+Pterygota is the absence of intrinsicantennalmuscles, which connect theantennomeresinentognaths,myriapods,andcrustaceans.For this reason, the whole group is often termed theAmyocerata,meaning "lacking antennal muscles".
However, the Zygentoma are now considered more closely related to the Pterygota than to the Archaeognatha,[4]thus rendering even the amyocerate apterygotes paraphyletic, and resulting in the dissolution of Thysanura into two separate monophyletic orders.
References
edit- ^Hoell, H.V.; Doyen, J.T. & Purcell, A.H. (1998).Introduction to Insect Biology and Diversity(2nd ed.). Oxford University Press. p. 320.ISBN978-0-19-510033-4.
- ^ab"Subclass Apterygota Brauer 1885 (insect)".Fossilworks.Retrieved17 December2021.
- ^WoRMS (2019). Apterygota. Accessed at:http://www.marinespecies.org/aphia.php?p=taxdetails&id=151153on 2019-01-22
- ^abA. Blanke, M. Koch, B. Wipfler, F. Wilde, B. Misof (2014) Head morphology ofTricholepidion gertschiindicates monophyletic Zygentoma. Frontiers in Zoology 11:16 doi:10.1186/1742-9994-11-16
- ^Yanoviak, SP; Kaspari, M; Dudley, R (2009)."Gliding hexapods and the origins of insect aerial behaviour".Biol Lett.5(4):510–2.doi:10.1098/rsbl.2009.0029.PMC2781901.PMID19324632.
- ^Hoell, H.V.; Doyen, J.T. & Purcell, A.H. (1998).Introduction to Insect Biology and Diversity(2nd ed.). Oxford University Press. pp.333–340.ISBN978-0-19-510033-4.
- ^Insect Metamorphosis: From Natural History to Regulation of Development and Evolution
- Firefly Encyclopedia of Insects and Spiders,edited by Christopher O'Toole,ISBN1-55297-612-2,2002