endo means "within" and pterygos means "wing"
The name of this now-dominant and worldwide taxon is derived from the fact that the future wing tissue in larval instar are internal and develop during the resting pupal stage in which they are everted on to the surface of the body. The metamorphosis of these insects is divided into distinct stages: egg, larva, pupa, and adult. Another name for this taxon is Holometabola, refering to the complete metamorphosis. The key to the success of this group lies in the differentation in habits, structures, and food sources between the adult and preadult stages. The larvae are usually adapted to the food substrate, and are often more cryptic and sedentary than the adults. Being better fitted for these habits, the antennae, legs, and eyes of the larvae are usually smaller and markedly less complex.
The orthopterodean insect bodyplan is the basis of the primitive endopterygote. The mouthparts are mandibulate, but their structure can vary, depending on feeding habits. The genitalia of the male are basically like those of the Thysanura (firebrats, silverfish); the ovipositor is primitive and the larvae retain abdominal vesicles and styli. The adult has numerous malpighian tubules, and the nervous system consists of several ganglia in series. The higher the degree of changes in metamorphosis, the more of these trades are lost or modified. Most of the endopterygotes have wings as adults, but there are numerous exceptions. The wings, normally in two pairs, are primitively unequal, and in most orders the hindwings tend towards reduction. There is often a coupling mechanism, and the venation is generalized or reduced. The forewings or hindwings may be highly modified to act as balancers (in Diptera), elytra (in Coleoptera) or otherwise.
The phyletic relationships within this taxon are less confusing than they are within the Neoptera. Formerly, systematics saw this group as an polyphyletic assemblage, but recently views have changed because most interrelations have become much clearer. The main groups now recognized are; the Neuropteroidea (including the Megaloptera (dobsonflies and fishflies), Raphidioptera (snakeflies), Neuroptera (lacewings, antlions, owflies, etc.), Coleoptera (beetles), and Strepsiptera (twisted-wing parasites)); the Panorpoidea (including Mecoptera (scorpionflies), Siphonaptera (fleas), and Diptera (flies), Trichoptera (caddisflies) and Lepidoptera (moths and butterflies)); and the Hymenopteroidea (including the Hymenoptera (wasps, bees, ants, and sawflies)).