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 silverfish, Thermobia domestica
taxon links [up-->]Pterygota [up-->]Thysanura [up-->]Archaeognatha [down<--]Hexapoda Interpreting the tree
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This tree diagram shows the relationships between several groups of organisms.

The root of the current tree connects the organisms featured in this tree to their containing group and the rest of the Tree of Life. The basal branching point in the tree represents the ancestor of the other groups in the tree. This ancestor diversified over time into several descendent subgroups, which are represented as internal nodes and terminal taxa to the right.

example of a tree diagram

You can click on the root to travel down the Tree of Life all the way to the root of all Life, and you can click on the names of descendent subgroups to travel up the Tree of Life all the way to individual species.

For more information on ToL tree formatting, please see Interpreting the Tree or Classification. To learn more about phylogenetic trees, please visit our Phylogenetic Biology pages.

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Containing group: Hexapoda


Insects have a large number of unique, derived characteristics, although none of these are externally obvious in most species. These include (Kristensen, 1991):

Discussion of Phylogenetic Relationships

The relationships of primitively wingless insects to each other and to winged insects (pterygotes) is well established, with a few exceptions.

One notable feature linking Thysanura + Pterygota is the presence of two articulations on each mandible. Archaeognathans have only one mandibular condyle or articulation point; they are "monocondylic". Thysanura + Pterygota, with their two mandibular condyles, are sometimes called Dicondylia. The many other apomorphies linking Dicondylia are described in Kristensen (1991).

It is possible that the thysanurans are not themselves monophyletic; Thysanura (exclusive of the family Lepidothricidae) plus pterygotes may be monophyletic, with lepidothricids sister to this complex (Kristensen, 1991).

Other Names for Insecta


Beutel, R. G. and S. N. Gorb. 2001. Ultrastructure of attachment specializations of hexapods, (Arthropoda): evolutionary patterns inferred from a revised ordinal phylogeny. Journal of Zoological Systematics and Evolutionary Research 39:177-207.

Bitsch, J. and A. Nel. 1999. Morphology and classification of the extinct Archaeognatha and related taxa (Hexapoda). Annales de la Société entomologique de France 35:17-29.

Boudreaux, H. B. 1979. Arthropod Phylogeny with Special Reference to Insects. New York, J. Wiley.

Carpenter, F. M. 1992. Superclass Hexapoda. Volumes 3 and 4 of Part R, Arthropoda 4 of Treatise on Invertebrate Paleontology. Boulder, Colorado, Geological Society of America.

Carpenter, F. M. and L. Burnham. 1985. The geological record of insects. Annual Review of Earth and Planetary Sciences 13:297-314.

Caterino, M. S., S. Cho, and F. A. H. Sperling. 1999. The current state of insect molecular systematics: a thriving tower of Babel. Annual Review of Entomology 45:1–54.

Chapman, R. F. 1998. The Insects: Structure and Function. Cambridge University Press, Cambridge, U.K., New York.

Daly, H. V., J. T. Doyen, and A. H. Purcell III. 1998. Introduction to Insect Biology and Diversity, 2nd edn. Oxford University Press, Oxford.

Dindall, D. L. 1990. Soil Biology Guide. New York, John Wiley & Sons.

Engel, M. S. and D. A. Grimaldi. 2004. New light shed on the oldest insect. Nature 427:627-630.

Evans, H. E. 1993. Life on a Little-Known Planet. New York, Lyons & Burford.

Gereben-Krenn, B. A. and G. Pass. 2000. Circulatory organs of abdominal appendages in primitive insects (Hexapoda : Archaeognatha, Zygentoma and Ephemeroptera). Acta Zoologica 81:285-292.

Grimaldi, D. 2001. Insect evolutionary history from Handlirsch to Hennig, and beyond. Journal of Paleontology 75:1152-1160.

Grimaldi, D. and M. S. Engel. 2005. Evolution of the Insects. Cambridge University Press.

Hennig, W. 1981. Insect Phylogeny. New York, J. Wiley.

Kjer, K. M. 2004. Aligned 18S and insect phylogeny. Systematic Biology 53(3):506-514.

Klass, K. D. 1998. The proventriculus of the Dicondylia, with comments on evolution and phylogeny in Dictyoptera and Odonata (Insecta). Zoologischer Anzeiger 237:15-42.

Kristensen, N. P. 1975. The phylogeny of hexapod "orders". A critical review of recent accounts. Zeitschrift für zoologische Systematik und Evolutionsforschung 13:1–44.

Kristensen, N. P. 1981. Phylogeny of insect orders. Annual Review of Entomology 26:135-157.

Kristensen, N. P. 1995. Forty years' insect phylogenetic systematics. Zoologische Beiträge NF 36(1):83-124.

Kukalová-Peck, J. 1987. New Carboniferous Diplura, Monura, and Thysanura, the hexapod ground plan, and the role of thoracic lobes in the origin of wings (Insecta). Canadian Journal of Zoology 65:2327-2345.

Labandeira, C. C., and J. J. Sepkoski, jr. 1993. Insect diversity in the fossil record. Science 261:310–315.

Larink, O. 1997. Apomorphic and plesiomorphic characteristics in Archaeognatha, Monura, and Zygentoma. Pedobiologia 41:3-8.

Merritt, R. W. and K. W.Cummins, eds. 1984. An Introduction to the Aquatic Insects of North America, Second Edition. Kendall-Hunt.

Naumann, I. D., P. B. Carne, J. F. Lawrence, E. S. Nielsen, J. P. Spradberry, R. W. Taylor, M. J. Whitten and M. J. Littlejohn, eds. 1991. The Insects of Australia: A Textbook for Students and Research Workers. Volume I and II. Second Edition. Carlton, Victoria, Melbourne University Press.

Pass, G. 2000. Accessory pulsatile organs: Evolutionary innovations in insects. Annual Review of Entomology 45:495-518.

Snodgrass, R. E. 1935. Principles of Insect Morphology. McGraw-Hill, New York. 667 pp.

Snodgrass, R. E. 1952. A Textbook of Arthropod Anatomy. Comstock Publishing Associates, Ithaca, N.Y. 363 pp.

Stehr, F. W. 1987. Immature Insects, vol. 1. Dubuque, Iowa: Kendal/Hunt. 754 pp.

Stehr, F. W. 1991. Immature Insects, vol. 2. Dubuque, Iowa: Kendal/Hunt. 974 pp.

Wooton, R. J. 1981. Paleozoic insects. Annual Review of Entomology 26:319-344.

Information on the Internet

Internet directories:

Images and Other Media:

Fossil Insects:

Famous entomologists:

For young entomologists:

Title Illustrations
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Scientific Name Machilidae
Location USA: North Carolina: Durham
Comments Bristletail (Archaeognatha)
Specimen Condition Live Specimen
Image Use creative commons This media file is licensed under the Creative Commons Attribution License - Version 3.0.
Copyright © 2004 David R. Maddison
silverfish, Thermobia domestica
Scientific Name Thermobia domestica
Location Tucson, Arizona, USA
Comments Silverfish (Thysanura)
Image Use creative commons This media file is licensed under the Creative Commons Attribution License - Version 3.0.
Copyright © 2003 David R. Maddison
Scientific Name Lestidae
Location Zion National Park (Utah, USA)
Creator Photograph by Robert Potts
Specimen Condition Live Specimen
Source Coenagrionidae Family; Narrow-winged Damsel Fly
Source Collection CalPhotos
Copyright © California Academy of Sciences
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Citing this page:

Tree of Life Web Project. 2002. Insecta. Insects. Version 01 January 2002 (under construction). http://tolweb.org/Insecta/8205/2002.01.01 in The Tree of Life Web Project, http://tolweb.org/

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This page is a Tree of Life Branch Page.

Each ToL branch page provides a synopsis of the characteristics of a group of organisms representing a branch of the Tree of Life. The major distinction between a branch and a leaf of the Tree of Life is that each branch can be further subdivided into descendent branches, that is, subgroups representing distinct genetic lineages.

For a more detailed explanation of the different ToL page types, have a look at the Structure of the Tree of Life page.

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