BristletailsInsects
The Archaeognatha are an order of apterygotes, known by various common names such as jumping bristletails. Among extant insect taxa they are some of the most evolutionarily primitive; they appeared in the Middle Devonian period at about the same time as the arachnids.
Scientific name: Archaeognatha
Rank: Order
Higher classification: Insect Bristletail, (order Archaeognatha), any of approximately 350 species of primitive wingless insects that measure from 5 to 20 mm (0.2 to 0.8 inch) in length when they are fully grown and have three slender bristlelike appendages at the tip of the abdomen.
Bristletails have small compound eyes and external mouthparts. Some species have scales covering the body. Young bristletails resemble adults except in size.
Sexual maturity is attained in two to three years, and the life span of some species may be as long as seven years. A bristletail molts as many as 35 times during its life (three to five times per year). Bristletails eat starchy material, often causing damage to books and papers.
Bristletails historically were placed in the order Thysanura, which has since been replaced by the orders Archaeognatha (also called Microcoryphia) and Zygentoma (silverfish and firebrats).
One of the oldest known insect fossils for which there is significant remaining structure (head and thorax fragments) is a bristletail, estimated to be 390 to 392 million years old. It was discovered on the north shore of Gaspé Bay, Quebec, Canada, at a site that was only 10° above the Equator during the Devonian time of this insect.
Biology of Bristletails
Description
Archaeognatha are small insects with elongated bodies and backs that are arched, especially over the thorax. They have three long tail-like structures, of which the lateral two are cerci, while the medial filament, which is longest, is an epiproct.
The antennae are flexible. The two large compound eyes meet at the top of the head, and there are three ocelli. The mouthparts are partly retractable, with simple chewing mandibles and long maxillary palps.[1]:341–343
Archaeognatha differ from Zygentoma in various ways, such as their relatively small head, their bodies being compressed laterally (from side to side) instead of flattened dorsiventrally, and in their being able to use their tails to spring up to 30 cm (12 in) into the air if disturbed.
They also are unique among insects in possessing small, articulated "styli" on the hind (and sometimes middle) coxae and on sternites 2 to 9, which some authorities consider to be vestigial appendages. They have paired eversible membranous vesicles through which they absorb water.
Etymology
The name Archaeognatha is derived from Greek, ἀρχαῖος, (archaios) meaning ancient and γνάθος (gnathos) meaning "jaw". This refers to the articulation of the mandibles, which have a single phylogenetically primitive condyle each, where all more derived insects have two.
An alternative name, Microcoryphia, comes from the Greek μικρός (mikros), meaning "small", and κορυφή (koryphē), which in context means "head".
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