Plecoptera
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[Photo] Picture of a member of the family Pteronarcyidae (Plecoptera). Author = Tr??pas

Plecoptera are an order of insects, commonly known as stoneflies. There are some 1,700 recorded species worldwide.

The nymphs are aquatic and live in the benthic zone of lakes and streams. Nymphs of this order are hunters of other aquatic arthropods or shredders of large organic particles, such as leaves. Some also graze on benthic algae. They undergo many molts as aquatic nymphs (10 instars?) before emerging and becoming terrestrial as adults.

The name comes from the Greek pleikein ("braided") and ptera ("wing"). They possess two pairs of wings which are membranous and fold flat over the back. Both nymphs and adults have long paired cerci projecting from the tip of their abdomens.

A few wingless species such as Capnia lacustra are the only known insects that are fully aquatic from birth to death [1].

They are believed to be one of the most primitive groups of insects with close relatives identified from the Carboniferous and Lower Permian geological periods.

Plectoptera 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 [2].

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

Systematics
This list has been adapted from the Tree of Life Web [3].

Antarctoperlaria
- Eustheniidae
- Diamphipnoidae
- Austroperlidae
- Gripopterygidae

Arctoperlaria
- Scopuridae
- Taeniopterygidae (ca. 75 species) - winter stoneflies
- Notonemouridae
- Nemouridae (ca. 400 species) - spring stoneflies
- Capniidae (ca. 300 species) - small winter stoneflies
- Leuctridae - rolled-winged stoneflies
- Pteronarcyidae (ca. 12 species) - salmonflies, giant stoneflies
- Styloperlidae (ca. 7 species)
- Peltoperlidae (ca. 50 species) - roachlike stoneflies
- Perlodidae (250+ species)
- Perlidae (ca. 400 species) - common stoneflies
- Chloroperlidae (100+ species) - green stoneflies

http://en.wikipedia.org/wiki/Plecoptera

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