name = Small winter stoneflies
image_width = 240px
image_caption = "
Eocapnia nivalis" on the snow in Nagano( Japan)
familia = Capniidae
subdivision = 17-20, see text
Capniidae, the small winter stoneflies, are a family of
insects in the stoneflyorder (Plecoptera). They constitute one of the largest stonefly families, containing some 300 speciesdistributed 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
monotypicas to subfamily, with the Capniinae being inserted at that rank. However, this is rather pointless; in any case the phylogeny, systematicsand taxonomyof 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.
type genus"Capnia" is probably not monophyleticand 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:
Suspected clade/subfamily 1
Suspected clade 2/subfamily Capniinae "sensu stricto"
Capnia" ( paraphyletic)
Incertae sedis" as to clade 1 or 2
* (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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