Exopterygota ("external winged forms") develop wings on the outside of their bodies without going through a true pupal stage, though a few have something resembling a pupa (e.g., Aleyrodidae ). Ephemeroptera (mayflies) and Odonata (dragonflies and damselflies) also have gradual wing development, this being a plesiomorphic trait.
They are unique among insect orders in having a fully winged terrestrial preadult stage, the subimago, which moults into a sexually mature adult, the imago . Mayflies "hatch" (emerge as adults) from spring to autumn, not necessarily in May, in enormous numbers.
They are distinguished from the Endopterygota (or Holometabola) by the way in which their wings develop. Endopterygota (meaning literally "internal winged forms") develop wings inside the body and undergo an elaborate metamorphosis involving a pupal stage.
Grimaldi and Engel, reviewing the phylogeny in 2005, commented that many cladistic studies had been made with no stability in Ephemeroptera suborders and infraorders; the traditional division into Schistonota and Pannota was wrong because Pannota is derived from the Schistonota.
For extinct groups and possible future splits, see text. The Exopterygota ( Ancient Greek ἔξω (éxō, “outside”) + πτερόν (pterón, “wing”) + New Latin -ota (“having”)), also known as Hemipterodea, are a superorder of insects of the subclass Pterygota in the infraclass Neoptera, in which the young resemble adults ...
They are distinguished from the Endopterygota (or Holometabola) by the way in which their wings develop. Endopterygota (meaning literally "internal winged forms") develop wings inside the body and undergo an elaborate metamorphosis involving a pupal stage. Exopterygota ("external winged forms") develop wings on the outside of their bodies without going through a true pupal stage, though a few have something resembling a pupa (e.g., Aleyrodidae ).
The nymphs develop gradually into adults through a process of moulting. The Exopterygota are a highly diverse insect superorder, with at least 130,000 living species divided between 15 orders. They include cockroaches, termites, grasshoppers, thrips, lice and stick insects, among many other types of insects.
Exopterygota ("external winged forms") develop wings on the outside of their bodies without going through a true pupal stage , though a few have something resembling a pupa (e.g., Aleyrodidae ). Ephemeroptera (mayflies) and Odonata (dragonflies and damselflies) also have gradual wing development, this being a plesiomorphic trait.
It is realized that some presumed Exopterygota may in fact be basal neopterans, making the superorder paraphyletic .
The word Exopterygota refers to the development of the wings outside the body. Insects that develop in this way are said to show incomplete metamorphosis. In the orders of insects which make up the Exopterygota , the larvae are usually called nymphs.
Dragonfly nymphs are aquatic and must climb out of the water in order to moult in to the final, more familiar, adult form. The wing buds are clearly visible as two flat structures on the back of this dragonfly exuviae (moulted skin). Endopterygota. Incomplete metamorphosis. Insects.
Adult Atalophlebia with the cylindrical dorsal or turban eyes visible. Adult mayflies, or imagos, are relatively primitive in structure, exhibiting traits that were probably present in the first flying insects. These include long tails and wings that do not fold flat over the abdomen.
Along with caddisfly larvae and gastropod molluscs, the grazing of mayfly nymphs has a significant impact on the primary producers, the plants and algae, on the bed of streams and rivers. The nymphs are eaten by a wide range of predators and form an important part of the aquatic food chain.
Mayfly nymphs may serve as hosts for parasites such as nematodes and trematodes.
A study in laboratory simulated streams revealed that the mayfly genus Centroptilum increased the export of periphyton, thus indirectly affecting primary production positively , which is an essential process for ecosystems. The mayfly can also reallocate and alter the nutrient availability in aquatic habitats through the process of bioturbation. By burrowing in the bottom of lakes and redistributing nutrients, mayflies indirectly regulate phytoplankton and epibenthic primary production. Once burrowing to the bottom of the lake, mayfly nymphs begin to billow their respiratory gills. This motion creates current that carries food particles through the burrow and allows the nymph to filter feed. Other mayfly nymphs possess elaborate filter feeding mechanisms like that of the genus Isonychia. The nymph have forelegs that contain long bristle-like structures that have two rows of hairs. Interlocking hairs form the filter by which the insect traps food particles. The action of filter feeding has a small impact on water purification but an even larger impact on the convergence of small particulate matter into matter of a more complex form that goes on to benefit consumers later in the food chain.
The abdomen is long and roughly cylindrical, with ten segments and two or three long cerci (tail-like appendages) at the tip. Uniquely among insects, mayflies possess paired genitalia, with the male having two aedeagi (penis-like organs) and the female two gonopores (sexual openings).
Top right: Subimago of Leptophlebia marginata. Bottom: Nymph of the mayfly Cloeon dipterum, showing seven pairs of gills along the sides of the abdomen. Immature mayflies are aquatic and are referred to as nymphs or naiads. In contrast to their short lives as adults, they may live for several years in the water.
Over 3,000 species of mayfly are known worldwide, grouped into over 400 genera in 42 families . Mayflies exhibit a number of ancestral traits that were probably present in the first flying insects, such as long tails and wings that do not fold flat over the abdomen.