The Entognatha is a class

Class (biology)

In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...

 of ametabolous arthropod

Arthropod

An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s, which, together with insect

Insect

Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s, makes up the subphylum Hexapoda

Hexapoda

The subphylum Hexapoda constitutes the largest grouping of arthropods and includes the insects as well as three much smaller groups of wingless arthropods: Collembola, Protura, and Diplura . The Collembola are very abundant in terrestrial environments...

. Their mouthparts are entognathous, meaning they are retracted within the head. Entognatha are apterous, meaning they lack wings

Insect wing

Insects are the only group of invertebrates known to have evolved flight. Insects possess some remarkable flight characteristics and abilities, still far superior to attempts by humans to replicate their capabilities. Even our understanding of the aerodynamics of flexible, flapping wings and how...

. The class contains three orders

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

: Collembola (springtail

Springtail

Springtails form the largest of the three lineages of modern hexapods that are no longer considered insects...

s), Diplura and Protura. These three groups were historically united with the order Thysanura

Thysanura

Thysanura is an order of insects, encompassing silverfish and firebrats, known for their three long caudal filaments.The families Machilidae and Meinertellidae of the jumping bristletails were once included with Thysanura....

 to form the class Apterygota

Apterygota

The name Apterygota is sometimes applied to a subclass of small, agile insects, distinguished from other insects by their lack of wings in the present and in their evolutionary history...

, but it has since been recognized that the hexapodous condition of these animals has evolved independently from that of insects, and independently within each order.