Plecoptera

Plecoptera are an order of insects, commonly known as stoneflies. There are some 3,500 described species worldwide, and new ones are still being discovered. Although stoneflies are found worldwide, they are absent from Antarctica. Stoneflies are believed to be one of the most primitive groups of Neoptera, with close relatives identified from the Carboniferous and Lower Permian geological periods, while true stoneflies are known from fossils only a bit younger. The modern diversity however apparently is of Mesozoic origin.

Plecoptera are found in both the Southern and Northern hemispheres, and the populations are quite distinct although the evolutionary evidence suggests that species may have crossed the equator on a number of occasions before once again becoming geographically isolated.

All species of Plecoptera are intolerant of water pollution and their presence in a stream or still water is usually an indicator of good or excellent water quality.

Description and ecology

Stoneflies have a generalised anatomy, with few specialised features. They have simple mouthparts with chewing mandibles, long, multi-segmented antennae, large compound eyes and two or three ocelli. The legs are robust, with each ending in two claws. The abdomen is relatively soft, and may include remnants of the nymphal gills even in the adult. Both nymphs and adults have long paired cerci projecting from the tip of their abdomens.

The name "Plecoptera" literally means "braided-wings", from the Ancient Greek plekein (πλέκειν, "to braid") and pteryx (πτέρυξ, "wing"). This refers to the complex venation of their two pairs of wings, which are membranous and fold flat over the back. Stoneflies are generally not strong fliers, and some species are entirely wingless.

A few wingless species such as the Lake Tahoe Benthic Stonefly ("Capnia" lacustra) or Baikaloperla are the only known insects, perhaps with the exception of Halobates, that are exclusively aquatic from birth to death. Some true water bugs (Nepomorpha) may also be fully aquatic for their entire life, but can leave the water to travel.

The females lay hundreds or even thousands of eggs in a ball which they initially carry about on their abdomen, and later deposit into the water. The eggs typically take two to three weeks to hatch, but some species undergo diapause, with the eggs remaining dormant throughout a dry season, and hatching only when conditions are suitable.

The Arctoperlaria, meanwhile, have been divided into two infraorders, the Euholognatha (or Filipalpia) and the Systellognatha (also called Setipalpia or Subulipalpia). This corresponds to the phylogeny, with one exception: the Scopuridae must be considered a basal family in the Arctoperlaria, not assignable to any of the infraorders. Alternatively, the Scopuridae were placed in an unranked clade "Holognatha" together with the Euholognatha (meaning approximately "advanced Holognatha"). But the Scopuridae do not appear significantly closer to the Euholognatha than to the Systellognatha.

In addition, not adopting the clades Antarctoperlaria and Holognatha allows for a systematic layout of the Plecoptera that adequately reproduces phylogeny, while retaining the traditional ranked taxa.

(Euholognatha)]] (Systellognatha)]] Basal lineages ("Antarctoperlaria")

Suborder Arctoperlaria

Footnotes

References

See also

Category:Orders of insects