Archaeognatha

From Wikipedia, the free encyclopedia

Archaeognatha

Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Archaeognatha Börner, 1904

Families

Machilidae
Meinertellidae

Archaeognatha is an order of wingless insects, also known as jumping bristletails. 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" and gnatha meaning "jaw". This refers to the articulation of the mandibles, which has a single condyle, where all higher insects have two. An alternate name, Microcoryphia comes from the Greek micro meaning "small" and coryphia meaning head.

The Order Archaeognatha has previously been combined with the Order Thysanura, or bristletails, both of which groups possess three-pronged tails comprising two cerci and an epiproct. Archaeognatha differ from Thysanura in being able to use their tail to spring up to 30 cm into the air. They are also unique in possessing small, articulated "styli" on the hind (and sometimes middle) coxae and sternites 2 to 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.