Capniidae


Capniidae

__NOTOC__Taxobox
name = Small winter stoneflies


image_width = 240px
image_caption = "Eocapnia nivalis" on the snow in Nagano (Japan)
regnum = Animalia
phylum = Arthropoda
subphylum = Hexapoda
classis = Insecta
subclassis = Pterygota
infraclassis = Neoptera
superordo = Exopterygota
ordo = Plecoptera
subordo = Arctoperlaria
infraordo = Euholognatha
familia = Capniidae
familia_authority =
subdivision_ranks = Genera
subdivision = 17-20, see text

Capniidae, the small winter stoneflies, are a family of insects in the stonefly order (Plecoptera). They constitute one of the largest stonefly families, containing some 300 species distributed throughout the Holarctic. Their closest relatives are the rolled-winged stoneflies (Leuctridae). [Nelson (1996a,b)]

Many species are endemic to small ranges, perhaps due to the family's tendency to evolve tolerance for cold (isolating populations in mountain valleys) and winglessness (inhibiting dispersal)Nelson (1996b)] . Indeed, some wingelss Capniidae, e.g. the Lake Tahoe Benthic Stonefly (""Capnia" lacustra" ["Capnia" is not monophyletic and this species is suspected to belong elsewhere (see "Systematics and taxonomy" section)] ) or "Baikaloperla", spend their entire lives underwater and do not disperse from their native lakes at all [Holst (2000)] .

Description and ecology

Adult Capniidae are, as their commnon name implies, usually small Plecoptera; while most are less than 1 cm long with some measuring just 4 mm as adults, a few can get as large as 25 mm (1 inch) however. The adults emerge form the water in winter and are often found walking around on the snow. Characteristic are the wings with at most one cubital crossvein, and the paraprocts (anal lobes) whose inner lobes form a tube closed on the underside by the outer lobes.

Nymphs of small winter stoneflies typically have a very elongated and slender body, similar to those of rolled-winged stoneflies (Leuctridae). However, the groove along the abdomen, from segment 1 to 9, is generally very pronounced.

The nymphs dwell in the hyporheic zone, the interface between stream water and groundwater. Only immediately before moulting into the adult form will the nymphs move out of the substrate and appear on the stream bed. Thus, although they may be plentiful in clean rivers and streams, they are seldom encountered in standard samples of benthos.

ystematics and taxonomy

Often, the family Capniidae is considered monotypic as to subfamily, with the Capniinae being inserted at that rank. However, this is rather pointless; in any case the phylogeny, systematics and taxonomy of the small winter stoneflies are highly confused. There appear to be two very basal genera and presumably two larger clades which conceivably could be considered subfamilies. However, the phylogeny of the Capniidae is by no means robustly resolved, with about one-third of the named genera of uncertain position. Hence, any subdivision beyond the generic level is premature.

Furthermore, the type genus "Capnia" is probably not monophyletic and in serious need of splitting up. The type species "Capnia nigra" and its closest relatives would retain their genus name; they are closely related to "Capnura". The North American species at least for the largest part are closer to "Mesocapnia"; other "Capnia" are closest to "Bolshecapnia" as it seems. Finally, there is a fourth group of rather uncertain position in the main assemblage of Capniidae.

A rough layout of the suspected phylogeny can be given as follows:

Basal genera
* "Isocapnia"
* "Paracapnia"

Suspected clade/subfamily 1
* "Nemocapnia"
* "Capnioneura"
* "Eucapnopsis"

Suspected clade 2/subfamily Capniinae "sensu stricto"
* "Bolshecapnia"
* "Allocapnia"
* "Baikaloperla"
* "Capnia" (paraphyletic)
* "Capnura"
* "Utacapnia"
* "Mesocapnia"

"Incertae sedis" as to clade 1 or 2
* "Allocapniella"
* "Capniella"
* "Capnopsis"
* "Eocapnia"
* "Takagripopteryx"

Footnotes

References

* (19961): [http://tolweb.org/Plecoptera/8245/1996.01.01 Plecoptera. Stoneflies] . Version of 1996-JAN-01. Retrieved 2008-JUL-31.
* (1996b): [http://tolweb.org/Capniidae/13943/1996.01.01 Capniidae. Winter Stoneflies] . Version of 1996-JAN-01. Retrieved 2008-JUL-31.


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