Archaeognatha

Archaeognatha Temporal range: Devonian–Recent[1] PreЄ Є O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Subclass:	Monocondylia
Order:	Archaeognatha
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.

There are approximately 350 species in the two families, distributed worldwide. 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.

Description

Archaeognaths are small insects with elongated bodies bent into an arch shape and three long tail-like structures. They have flexible antennae, large compound eyes that meet at the top of the head, and three ocelli. Their mouthparts are partially retractable, with simple chewing mandibles and long maxillary palps.^[2]

Archaeognatha differ from Thysanura in being able to use their tail to spring up to 30 centimetres (12 in) 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 membranous vesicles through which they absorb water.

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.

Biology

Archaeognaths are found in a wide range of habitats, and are unusual among insects in that they can even be found in the Arctic where they live in leaf litter and rock crevices. While most species are found in moist soil, others have adapted to chaparral, and even sandy deserts. They feed primarily on algae, but also lichens, mosses, or decaying organic materials.

During courtship, the males spin a thread from their abdomen, attach one end to the substrate, and string packages of sperm (spermatophores) along it. After a series of courtship dances, the female picks up the spermatophores and places them on her ovipositor. The female then lays a batch of around 30 eggs in a suitable crevice. The young resemble the adults, and take up to two years to reach sexual maturity. Unlike most insects, the adults continue to moult after reaching adulthood, and typically mate once at each instar. Archaeognaths may have a total lifespan of up to four years, longer than many larger insects.^[2]

References

1. ^ Hoell, H.V., Doyen, J.T. & Purcell, A.H. (1998). Introduction to Insect Biology and Diversity, 2nd ed.. Oxford University Press. p. 320. ISBN 0-19-510033-6. 
2. ^ ^{a b} Hoell, H.V., Doyen, J.T. & Purcell, A.H. (1998). Introduction to Insect Biology and Diversity, 2nd ed.. Oxford University Press. pp. 341–343. ISBN 0-19-510033-6. 

• Christopher O'Toole (2002). Firefly Encyclopedia of Insects and Spiders. ISBN 1-55297-612-2. 

External links

• Archaeognatha - Tree of Life Web Project
• Microcoryphia Virginia Polytechnic Institute and State College Department of Entomology