Archaeognatha

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iArchaeognatha

Scientific classification

Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Subclass:	Apterygota
Order:	Archaeognatha

Families

Archaeognatha is an order of the class Insecta, also known as the jumping bristletails, which have previously been combined with the order Thysanura, or bristletails; both groups are so named because of their three-pronged tails, but Archaeognatha can use the tail to spring themselves into the air short distances (up to 30 cm). An alternate name is the Microcoryphia from micro, small and coryphia, head. They are among the least evolutionarily changed insects, appearing in the Devonian period along with the Arachnids. The name Archaeognatha is derived from Greek. Archaeos meaning ancient is combined with gnatha meaning jaw. This refers to the articulation of the mandibles, which has a single condyle, where all higher insects have two. They are also unique in possessing small, articulated "styli" on the hind (and sometimes middle) coxae and sternites 2 through 9, which are sometimes considered to be rudimentary appendages, as well as paired eversible vesicles (membranous water-absorbing organs). Further unusual features are that the abdominal sternites are each composed of three sclerites, and they cement themselves to the substrate before molting. Like Thysanura, the body is covered with scales, with a thin exoskeleton that is susceptible to dehydration.

There are approximately 350 species in the two families. They are distributed worldwide, and unusual in the insect world in that they can even be found in the Arctic where they live in leaf litter and rock crevices. They feed primarily on algae, but also lichens, mosses, or decaying organic materials.

There are no species at current conservation risk, though the order is one of the most poorly-studied among insects, and therefore it may simply be that no one has yet recognized that any species are at risk.