| Entognatha | |
|---|---|
_micrograph.jpg) | |
| Proturan specimen (Acerentomon sp.) | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Clade: | Pancrustacea |
| Subphylum: | Hexapoda |
| Class: | Entognatha |
| Groups included | |
| |
| Cladistically included but traditionally excluded taxa | |
Insecta (insects) | |
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TheEntognatha, fromAncient Greek ἐντός (entós), meaning "inside", and γνάθος (gnáthos), meaning "jaw", are aclass of wingless andametabolousarthropods, which, together with theinsects, makes up the subphylumHexapoda.[1][2] Theirmouthparts are entognathous, meaning that they are retracted within the head, unlike the insects.[1] Entognatha areapterous, meaning that they lackwings. The class contains threeorders: Collembola (springtails, 9000 species),[3]Diplura ("two-tail", 1000 species)[4] andProtura ("first-tail", 800 species).[5][1][2] These three groups were historically united with the now-obsolete orderThysanura to form the classApterygota, but it has since been recognized that the hexapodous condition of these animals has evolved independently from that of insects, and independentlywithin each order.[6] The orders might not be closely related, and Entognatha is now considered to be aparaphyletic group.[2]
These minutearthropods are apterous, unlike some orders of insects that have lost theirwings secondarily (but are derived from winged ancestors). Their mouthparts are enclosed within a pouch in the head capsule, called the gnathal pouch, so only the tips of the mandibles and maxillae are exposed beyond the cavity.[1] This pouch is created in the embryo by a flap or lateral head sclerite near the mouth on each side of the head which fuses with the labium.[1] Other differences from insects are that eachantennal segment is musculated; in insects, only the two basal segments are. Sperm transfer is always indirect, and there is anovipositor in the females. Of the three orders, only collembolans possess eyes;[2] nevertheless, many collembolans are blind, and even whencompound eyes are present, there are no more than eightommatidia.
