Plecoptera

Stoneflies
Fossil range: 299–0 Ma
Permian - Recent
Adult of genus Eusthenia
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Hexapoda
Class: Insecta
Subclass: Pterygota
Infraclass: Neoptera
Superorder: Exopterygota
Order: Plecoptera
Burmeister, 1839
Suborders

Arctoperlaria
and see text

Plecoptera are an order of insects, commonly known as stoneflies. There are some 3,497 described species worldwide[1], and new ones are still being discovered. Although stoneflies are found worldwide, they are absent from Antarctica [2]. 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.[3]

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[4].

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

Stonefly nymph
Stonefly adult

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.[5]

The name "Plecoptera" literally means "braided-wings", from the Ancient Greek plekein (πλέκειν, "to braid") and pteryx (πτέρυξ, "wing")[6]. 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[7]) or Baikaloperla are the only known insects that are exclusively aquatic from birth to death[8]. 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.[5]

The nymphs are aquatic and live in the benthic zone of well-oxygenated lakes and streams. A few species found in New Zealand and nearby islands have terrestrial nymphs, but even these inhabit only very moist environments. The nymphs physically resemble wingless adults, but often have external gills, which may be present on almost any part of the body. In addition, they can also respire through the general body surface, and some even lack gills altogether. Most species are herbivorous as nymphs, feeding on submerged leaves and benthic algae, but many are hunters of other aquatic arthropods.[5]

The insects remain in the nymphal form for one to four years, depending on species, and undergo anything from 12 to 33 molts before emerging and becoming terrestrial as adults. The adults generally only survive for a few weeks, and emerge only during specific times of the year. Some do not feed at all, but those that do are herbivorous.[5]

Systematics

Traditionally, the stoneflies were divided into two suborders, the "Antarctoperlaria" (or "Archiperlaria") and the Arctoperlaria. However, the former simply consists of the two basalmost superfamilies of stoneflies, which do not seem to be each other's closest relatives. Thus, the "Antarctoperlaria" are not considered a natural group (despite some claims to the contrary).[9]

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.[10]

Adult of family Taeniopterygidae (Euholognatha)
Adult of family Perlidae (Systellognatha)

Basal lineages ("Antarctoperlaria")

Suborder Arctoperlaria

Footnotes

  1. ↑ Fochetti and de Figueroa, 2008
  2. ↑ Brittain, 1987
  3. ↑ Zwick (2000)
  4. ↑ Hynes (1993), Zwick (2000
  5. ↑ 5.0 5.1 5.2 5.3 Hoell, H.V., Doyen, J.T. & Purcell, A.H. (1998). Introduction to Insect Biology and Diversity, 2nd ed.. Oxford University Press. pp. 383–386. ISBN 0-19-510033-6. 
  6. ↑ Woodhouse (1910)
  7. ↑ The genus Capnia is not monophyletic and this species is suspected to belong elsewhere: Nelson (1996a)
  8. ↑ Holst (2000)
  9. ↑ Nelson (1996b)
  10. ↑ Nelson (1996b), Zwick (2000)

References