Archaeognatha

Definition

An order of wingless insects (apterygotes) characterized by a humped thorax, large compound eyes that meet at the top of the head, three long caudal filaments (two cerci plus a median epiproct), and the ability to spring into the air by flexing the abdomen against the substrate. They are among the most evolutionarily basal of extant insect lineages, with fossil records extending to the Middle Devonian (~400 million years ago).

Etymology

From Greek archaios (ancient) + gnathos (jaw), referring to the primitive, partly exposed mandibular articulation (dicondylic) characteristic of this group.

Example

The jumping bristletail Machilis maritima, a common archaeognathan of European coastlines, illustrates the order's characteristic saltatorial escape response and preference for rocky littoral microhabitats.

Synonyms

• Microcoryphia

Related Terms

• Apterygote
• Zygentoma
• bristletail
• dicondylic mandible
• Epiproct
• cercus
• aptery
• Paleoptera
• basal insect

Usage Notes

The alternative name Microcoryphia (Greek: small head) reflects historical emphasis on the relatively small head capsule compared to the humped thorax; Archaeognatha is now preferred. Distinguished from the superficially similar Zygentoma (silverfish and firebrats) by the presence of compound eyes, ability to jump, and the epiproct being nearly as long as the cerci. The spelling 'Archeognatha' (without the second 'a') is a common misspelling; the correct form follows the Greek root archaios.