Archaeognatha

Sea bristletails Petrobius maritimus, photographed by Jymm.

Belongs within: Panhexapoda.
Contains: Meinertellidae.

The Archaeognatha, bristletails, are a group of wingless insects with an arched thorax modified for jumping. Recent species are divided between the families Meinertellidae and Machillidae, with the Machilidae having urosternites bearing a well-developed median sclerite and two pairs of exsertile vesicles on urosternites II–V (Ferguson 1990).

Bouncing bristletails!
Published 25 June 2007

The first time I ever saw an archaeognathan, I found it mixed in a specimen vial with a bunch of harvestmen. Archaeognatha are one of the few living orders of wingless insects. In fact, under the current most-commonly-used definition for Insecta (which excludes the entognathous hexapods such as Collembola), Archaeognatha are the basalmost living order. As such, I was pretty excited to finally see one, even if only in the corpse. Archaeognathans are also referred to as bristletails in reference to the long cerci extending behing the abdomen.

The first feature that grabs the attention is the distinct hump that the back makes. This hump contains muscles for the archaeognathan to rapidly bend the abdomen downwards, pushing itself into the air and jumping up to 10cm high. Archaeognathans also have very large forward-facing compound eyes that actually meet in the middle. The maxillary palps are very large and could almost be mistaken for an extra pair of legs coming off the head.

If you want to see what makes archaeognathans really cool, though, you’ll have to look a little closer. As befits the basalmost insect order, they retain a few uber-primitive features that have disappeared from other modern insects. They are the only modern insects with monocondylic mandibles—i.e. the mandibles have only one condyle (the socket where they attach and articulate with the head). All other insects have two. And if you were to look underneath the abdomen, you would see that each segment bears a pair of small pointed styles. These styles are moveable by muscles, and are thought to represent reduced legs. Let me repeat that in italics for emphasis—reduced legs. Archaeognathans are the only insects sensu stricto with abdominal styles, though they are also present in diplurans and proturans, two entognathous hexapod orders (I have not been able to find any indication that the styles in these orders are mobile, however).

While they have a fairly wide distribution worldwide, archaeognathans do not appear to be abundant and are fairly localised. I have heard that California is fairly well-blessed with them (big ones, too), but here in Australia they are most abundant in the eastern states.

Systematics of Archaeognatha

Characters (from Ferguson 1990): Body form subcylindrical, thorax strongly arched; head hypognathous; eyes large, contiguous, with hundreds of ommatidia; vertex greatly reduced; frons large, with median ocellus; lateral ocelli large; mandibles primitive, consisting of a basal part with a single point of articulation to the cranium and a distal part with separate molar and incisor processes; palpus of maxillae with seven segments; labium with palpus of three unequal segments, the distal not greatly expanded apically; thoracic terga with very large paranotal lobes against sides; all leg segments essentially cylindrical; meso- and metathoracic coxae typically with styli (may be absent on mesothoracic coxa or both); femur and tibia large; tarsus with three tarsomeres; abdominal segments II–VII covered ventrally by three distinct sclerites; an anteromedial sternite and two lateral coxopodites; coxopodites of abdominal segments II–IX each with a posterolateral stylus; posterior edge of segments I–VII typically with one or two pairs of exsertile vesicles mesad of the styli.

<==Archaeognatha [Machilida, Machiloidea, Microcoryphia, Monocondylia]
    |  i. s.: Triassomachilis Sharov 1948KS02 [TriassomachilidaeGE05]
    |           `--T. uralensis Sharov 1948K03
    |         Ditrigoniophthalmus oreophilusSBG11
    |--Dasyleptidae [Cercopodata, Monura]R02
    |    |--Leoidodasypus sharouiRJ93
    |    `--Dasyleptus Brongniart 1885FT05
    |         |--D. brongniarti Sharov 1957K-P83
    |         `--D. sharoviGE05
    `--+--MeinertellidaeR02
       `--MachilidaeR02
            |--Dilta littoralisGEW01, MG06
            |--Petridiobus arcticusF90
            |--Mesomachilis nearcticusF90
            |--Mixomachilis remingtoniF90
            |--Neomachilis halophilusF90
            |--Trigoniophthalmus Verhoeff 1910F90
            |    `--T. alternatus (Silvestri 1904)F90
            |--Pedetontus Silvestri 1911F90
            |    |--P. saltator Wygodzinsky & Schmidt 1980F90
            |    `--P. unimaculatusR02
            |--Machilis Latreille 1802L02
            |    |--*M. polypoda [=Lepisma polypoda]L02
            |    |--M. strenuvaF90
            |    `--M. variabilisLNM91
            `--Petrobius Leach 1908F90
                 |--P. brevistylis Carpenter 1913 [incl. P. canadensis Paclt 1969]F90
                 |--P. calcaratus Silvestri 1911F90
                 |--P. californicus Silvestri 1911F90
                 |--P. longicaudatusK-P83
                 |--P. maritimus Leach 1809F90
                 |--P. persquamosus Silvestri 1911F90
                 |--P. submutans Silvestri 1911F90
                 `--P. superior Silvestri 1911F90

*Type species of generic name indicated

References

[FT05] Fayers, S. R., & N. H. Trewin. 2005. A hexapod from the Early Devonian Windyfield Chert, Rhynie, Scotland. Palaeontology 48 (5): 1117–1130.

[F90] Ferguson, L. M. 1990. Insecta: Microcoryphia and Thysanura. In: Dindal, D. L. (ed.) Soil Biology Guide pp. 935–949. John Wiley & Sones: New York.

[GEW01] Giribet, G., G. D. Edgecombe & W. C. Wheeler. 2001. Arthropod phylogeny based on eight molecular loci and morphology. Nature 413: 157–161.

[GE05] Grimaldi, D., & M. S. Engel. 2005. Evolution of the Insects. Cambridge University Press: New York.

[K03] Kluge, N. J. 2003. About evolution and homology of genital appendages of insects. Trudy Russkogo Entomologicheskogo Obshestva [Proceedings of the Russian Entomological Society] 74: 3–16.

[KS02] Kluge, N. Yu., & N. D. Sinitshenkova. 2002. Order Ephemerida Latreille, 1810. The true mayflies (=Ephemeroptera Hyatt et Arms, 1891 (s. l.); =Euephemeroptera Kluge, 2000. In: Rasnitsyn, A. P., & D. L. J. Quicke (eds) History of Insects pp. 89–97. Kluwer Academic Publishers: Dordrecht.

[K-P83] Kukalová-Peck, J. 1983. Origin of the insect wing and wing articulation from the arthropodan leg. Canadian Journal of Zoology 61: 1618–1669.

[L02] Latreille, P. A. 1802. Histoire Naturelle, générale et particulière des crustacés et des insectes vol. 3. Familles naturelles des genres. F. Dufart: Paris.

[LNM91] Lawrence, J. F., E. S. Nielsen & I. M. Mackerras. 1991. Skeletal anatomy and key to orders. In: CSIRO. The Insects of Australia: A textbook for students and research workers 2nd ed. vol. 1 pp. 3–32. Melbourne University Press: Carlton (Victoria).

[MG06] Mallatt, J., & G. Giribet. 2006. Further use of nearly complete 28S and 18S rRNA genes to classify Ecdysozoa: 37 more arthropods and a kinorhynch. Molecular Phylogenetics and Evolution 40: 772–794.

[R02] Rasnitsyn, A. P. 2002. Subclass Lepismatona Latreille, 1804. The wingless insects (=Thysanura Latreille 1796, s. l.) In: Rasnitsyn, A. P., & D. L. J. Quicke (eds) History of Insects pp. 69–74. Kluwer Academic Publishers: Dordrecht.

[RJ93] Ross, A. J., & E. A. Jarzembowski. 1993. Arthropoda (Hexapoda; Insecta). In: Benton, M. J. (ed.) The Fossil Record 2 pp. 363–426. Chapman & Hall: London.

[SBG11] Staniczek, A. H., G. Bechly & R. J. Godunko. 2011. Coxoplectoptera, a new fossil order of Palaeoptera (Arthropoda: Insecta), with comments on the phylogeny of the stem group of mayflies (Ephemeroptera). Insect Systematics and Evolution 42: 101–138.

 

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