Oh my goodness! Unless you are a Tree of Life developer, you really shouldn't be here. This page is part of our beta test site, where we develop new features for the ToL, often messing up a thing or two in the process. Please visit the official version of this page, which is available here.

Under Construction

Containing group: Arthropoda

Introduction

While crustaceans are the dominant group of arthropods in marine environments, hexapods, including insects, rule the land. Their dominance among animals is evident in their numbers of species, with over 750,000 described (Wilson, 1988), as well as biomass (e.g. Fittkau and Klinge, 1973).

Hexapods include three orders of wingless arthropods (Collembola, Protura, Diplura), as well as the insects. The former orders are soil or litter dwellers. Collembola (springtails) are perhaps the most abundant arthropods on earth. Proturans are very small, pale arthropods that are rarely encountered. Diplurans include a few families of larger, pale arthropods that are frequently found in moist soils. The majority of hexapod species are insects, many of which are winged as adults.

Characteristics

The most distinctive feature of the hexapods is the reduction in walking appendages to six, with three body segments consolidating to form the thorax, which provides much of the locomotory ability of the animals. (This is in contrast to other arthropods, most of which have more than three pairs of legs.)

Discussion of Phylogenetic Relationships

The position of Diplura in the hexapods is unclear. Traditionally, it has been placed with the Collembola and Protura in a group called "Entognatha",

                     === Collembola
                  ===|
     ==Entognatha=|  === Protura
=====|            |
     |            ====== Diplura
     |
     =================== Insecta

so named because members of these three orders all have the base of the mouthparts internalized, so that the mandible and maxilla are partly contained within the head capsule. In addition to this derived similarity in mouth structure, these three orders share reduced Malpighian tubules and compound eyes. However, there is some evidence that diplurans may instead be the sister group of insects:

        === Collembola
     ===|
     |  === Protura
=====|
     |  === Diplura
     ===|
        === Insecta

Derived characteristics linking diplurans with insects include the presence of filiform cerci, and an extra set of nine single tubules in the axoneme of the sperm. For a more detailed discussion of the evidence, with additional references, see Kristensen (1991).

Other Names for Hexapoda

• Hexapods
• Insects, springtails, diplurans, and proturans

References

Arnett, R. H. 2000. American Insects: A Handbook of the Insects of America North of Mexico. CRC Press, Boca Raton, Fla.

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.

Bilinski, S. M. 1993. Structure of ovaries and oogenesis in entognathans (Apterygota). International Journal of Insect Morphology & Embryology 22:255-269.

Bitsch, C. and J. Bitsch. 1998. Internal anatomy and phylogenetic relationships among apterygote insect clades (Hexapoda). Annales de la Société Entomologique de France 34:339-363.

Bitsch, C. and J. Bitsch. 2000. The phylogenetic interrelationships of the higher taxa of apterygote hexapods. Zoologica Scripta 29:131-156.

Bitsch, C. and J. Bitsch. 2004. Phylogenetic relationships of basal hexapods among the mandibulate arthropods: a cladistics analysis based on comparative morphological characters. Zoologica Scripta 33(6):511-550.

Bitsch, J. 2001. The hexapod appendage: Basic structure, development and origin. Annales de la Société Entomologique de France 37: 175-193.

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

Carapelli, A., F. Frati, F. Nardi, R. Dallai, and C. Simon. 2000. Molecular phylogeny of the apterygotan insects based on nuclear and mitochondrial genes. Pedobiologia 44:361-373.

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.

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.

Deuve, T. 2001. The epipleural field in hexapods. Annales de la Societe Entomologique de France 37:195-231.

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

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

Fittkau, E. J. and H. Klinge. 1973. On biomass and trophic structure of the central Amazonian rain forest ecosystem. Biotropica 5:2-14.

Gaunt, M. W. and M. A. Miles. 2002. An insect molecular clock dates the origin of the insects and accords with palaeontological and biogeographic landmarks. Molecular Biology and Evolution 19(5):748-761.

Grandcolas, P., ed. 1997. Origin of Biodiversity in Insects: Phylogenetic Tests of Evolutionary Scenarios. Mémoires du Museum National d'Histoire Naturelle vol. 173. Éditions du Muséum, Paris. 354 pp.

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.

Gupta, A. P. 1979. Arthropod Phylogeny. Van Nostrand Reinhold, New York. 762 pp.

Haas, F., D. Waloszek, and R. Hartenberger. 2003. Devonohexapodus bocksbergensis, a new marine hexapod from the Lower Devonian Hunsrück Slates, and the origin of Atelocerata and Hexapoda. Organisms Diversity and Evolution 3:39-54.

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

Jamieson, B. G. M., R. Dallai, and B. Afzelius. 1999. Insects: Their Spermatozoa and Phylogeny. Science Publishers, Enfield, N. H.

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

Klass, K. D. and N. P. Kristensen. 2001. The ground plan and affinities of hexapods: Recent progress and open problems. Annales de la Société Entomologique de France 37:265-298.

Koch, M. 2000. The cuticular cephalic endoskeleton of primarily wingless hexapods: ancestral state and evolutionary changes. Pedobiologia 44:374-385.

Koch, M. 2001. Mandibular mechanisms and the evolution of hexapods. Annales de la Société Entomologique de France 37:129-174.

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. 1991. Phylogeny of extant hexapods. Pp. 125-140 in Insects of Australia: A Textbook for Students and Research Workers. Volume I and II. Second Edition. I. D. Naumann, P. B. Carne, J. F. Lawrence, E. S. Nielsen, J. P. Spradberry, R. W. Taylor, M. J. Whitten and M. J. Littlejohn eds. Carlton, Victoria, Melbourne University Press.

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

Kristensen, N. P. 1998. The groundplan and basal diversification of the hexapods. Pages 281-293 in Arthropod Relationships. R. A. Fortey and R. H. Thomas, eds. Systematics Association Special Volume Series 55. Chapman & Hall, London.

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.

Kukalová-Peck, J. 1991. Fossil history and the evolution of hexapod structures. Pages 141–179 in Insects of Australia: A Textbook for Students and Research Workers. Volume I and II. Second Edition. I. D. Naumann, P. B. Carne, J. F. Lawrence, E. S. Nielsen, J. P. Spradberry, R. W. Taylor, M. J. Whitten and M. J. Littlejohn eds. Carlton, Victoria, Melbourne University Press.

Labandeira, C.C. 1994. A compendium of fossil insect families. Milwaukee Public Museum Contributions in Biology and Geology 88:1-71.

Labandeira, C. C. 1997. Insect mouthparts: Ascertaining the paleobiology of insect feeding strategies. Annual Review of Ecology and Systematics 28:153-193.

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

Luan, Y., Y. Zhang, Q. Yue, J. Pang, R. Xie, and W. Yin. 2003. Ribosomal DNA gene and phylogenetic relationships of Diplura and lower hexapods. Science in China, Series C: Life Sciences 46(1):67-76.

Luan, Y., J. M. Mallatt, R. Xie, Y. Yang, and W. Yin. 2005. The phylogenetic positions of three basal-hexapod groups (Protura, Diplura, and Collembola) based on ribosomal RNA gene sequences. Molecular Biology and Evolution 2005 22(7):1579-1592.

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

Nardi, F., G. Spinsanti, J. L. Boore, A. Carapelli, R. Dallai, and F. Frati. 2003. Hexapod origins: monophyletic or paraphyletic? Science 299(5614):1887-1889.

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.

Ross, A. J. and E. A. Jarzembowski. 1993. Hexapoda. Pages 363-426 in The Fossil Record 2. M. J. Benton, ed. Chapman & Hall, London.

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.

Stys, P. and S. Bilinski. 1990. Ovariole types and the phylogeny of hexapods. Biological Reviews of the Cambridge Philosophical Society 65:401-429.

Stys, P., J. Zrzavy, and F. Weyda. 1993. Phylogeny of the Hexapoda and ovarian metamerism. Biological Reviews of the Cambridge Philosophical Society 68:365-379.

von Lieven, A. F. 2000. The transformation from monocondylous to dicondylous mandibles in the Insecta. Zoologischer Anzeiger 239:139-146.

Wheeler, W. C., M. Whiting, Q. D. Wheeler, and J. M. Carpenter. 2001. The phylogeny of the extant hexapod orders. Cladistics 17:113-169.

Willmann, R. 1998. Advances and problems in insect phylogeny. Pages 269–279 in Arthropod Relationships. R. A. Fortey and R. H. Thomas, eds. Systematics Association Special Volume Series 55. Chapman & Hall, London.

Wilson, E. O. 1988. The diversity of life. Pp. 68-78 in H. J. Blij (ed.), Earth '88. Changing Geographic Perspectives. National Geographic Society, Washington, D.C.

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

Information on the Internet

• Biodiversity Explorer: Hexapoda