The Capniidae, the small winter stoneflies, are a

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

s in the stonefly

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

(Plecoptera). It constitutes one of the largest stonefly families, containing some 300

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

distributed throughout the

holarctic The Holarctic realm is a biogeographic realm that comprises the majority of habitats found throughout the continents in the Northern Hemisphere. It corresponds to the floristic Boreal Kingdom. It includes both the Nearctic zoogeographical reg ...

. Their closest relatives are the rolled-winged stoneflies ( Leuctridae). Many species are

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

to small ranges, perhaps due to the family's tendency to evolve tolerance for cold (isolating populations in mountain valleys) and winglessness (inhibiting dispersal). Indeed, some wingless Capniidae – e.g. the

Lake Tahoe Lake Tahoe (; Washo language, Washo: ''dáʔaw'') is a Fresh water, freshwater lake in the Sierra Nevada of the Western United States, straddling the border between California and Nevada. Lying at above sea level, Lake Tahoe is the largest a ...

benthic stonefly ('' "Capnia" lacustra'', ''Capnia'' is not monophyletic and this species is suspected to belong elsewhere) or '' Baikaloperla'' spp. – spend their entire lifecycles under water and do not disperse from their native lakes at all.

Description and ecology

Adult Capniidae, as their common name implies, are typically small Plecoptera; while most are less than 1 cm long with some measuring just 4 mm as adults, a few are as large as at adulthood. The adults emerge from 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), the inner lobes of which form a tube closed on the underside by the outer lobes.

Nymph A nymph (; ; sometimes spelled nymphe) is a minor female nature deity in ancient Greek folklore. Distinct from other Greek goddesses, nymphs are generally regarded as personifications of nature; they are typically tied to a specific place, land ...

s of small winter stoneflies typically have very elongated and slender bodies, similar to those of Leuctridae. However, the groove along the

abdomen The abdomen (colloquially called the gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...

, from segment 1 to 9, is generally very pronounced. The nymphs dwell in the

hyporheic zone The hyporheic zone is the region of sediment and porous space beneath and alongside a stream bed, where there is mixing of shallow groundwater and surface water. The flow dynamics and behavior in this zone (termed hyporheic flow or underflow) is re ...

, the interface between stream water and

groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available fresh water in the world is groundwater. A unit ...

. Only immediately before

moulting In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is a process by which an animal casts off parts of its body to serve some beneficial purpose, either at ...

into the adult form will the nymphs move out of the substrate and appear on the

stream bed A streambed or stream bed is the bottom of a stream or river and is confined within a Stream channel, channel or the Bank (geography), banks of the waterway. Usually, the bed does not contain terrestrial (land) vegetation and instead supports d ...

. Thus, although they may be plentiful in clean rivers and streams, they are seldom encountered in standard samples of

benthos Benthos (), also known as benthon, is the community of organisms that live on, in, or near the bottom of a sea, river, lake, or stream, also known as the benthic zone.monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

as to

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zo ...

, with the Capniinae being inserted at that rank. However, this is rather pointless; in any case, the

phylogeny A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, M ...

systematics Systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: phylogenetic trees, phylogenies). Phy ...

, and

taxonomy image:Hierarchical clustering diagram.png, 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme o ...

of the small winter stoneflies are highly confused. There appear to be two very basal genera and presumably two larger

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

s which conceivably could be considered subfamilies, but 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. The

type genus In biological taxonomy, the type genus (''genus typica'') is the genus which defines a biological family and the root of the family name. Zoological nomenclature According to the International Code of Zoological Nomenclature, "The name-bearin ...

''Capnia'' has generally been considered

polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

. Three new or resurrected genera have recently been created, partially or wholly, from some of its species: '' Arsapnia'', '' Sierracapnia'', and '' Zwicknia''. In addition, seven ''Capnia'' species were previously included the genus '' Bolshecapnia'' when it was elevated from subgenus to genus, and three of those species were placed in the new genera '' Eurekapnia'' and '' Sasquacapnia'' in 2019.

Genera

These genera belong to the family Capniidae: * '' Allocapnia'' Claassen, 1928 * '' Apteroperla'' Matsumura, 1931 * '' Arsapnia'' Banks, 1897 * '' Baikaloperla'' Zapekina-Dulkeit & Zhiltzova, 1973 * '' Bolshecapnia'' Ricker, 1965 * '' Capnia'' Pictet, 1841 * '' Capniella'' Klapálek, 1920 * '' Capnioneura'' Ris, 1905 * '' Capnopsis'' Morton, 1896 * '' Capnura'' Banks, 1900 * '' Eocapnia'' Kawai, 1955 * '' Eucapnopsis'' Okamoto, 1922 * '' Eurekapnia'' Stark & Broome, 2019 * '' Isocapnia'' Banks, 1938 * '' Mesocapnia'' Raušer, 1968 * '' Nemocapnia'' Banks, 1938 * '' Paracapnia'' Hanson, 1946 * '' Sasquacapnia'' Baumann & Broome, 2019 * '' Sierracapnia'' Bottorff & Baumann, 2015 * '' Sinocapnia'' Murányi, Li & Yang, 2015 * '' Takagripopteryx'' Okamoto, 1922 * '' Utacapnia'' Gaufin, 1970 * '' Zwicknia'' Murányi, 2014

Extinct genera

* †'' Dobbertiniopteryx'' Ansorge, 1993 oooo Green Series, Germany, Early Jurassic (

Toarcian The Toarcian is, in the International Commission on Stratigraphy, ICS' geologic timescale, an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic. It spans the time between 184.2 Megaannum, Ma (million ...

), Daohugou, China, Middle/Late Jurassic * †'' Rovnocapnia'' Sinitshenkova 2009

Rovno amber Rovno amber, occasionally called Ukrainian amber, is amber found in the Rivne Oblast and surrounding regions of Ukraine and Belarus. The amber is dated between Late Eocene and Early Oligocene, and suggested to be contemporaneous to Baltic amber ...

, Ukraine,

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

References

{{Taxonbar, from=Q998398 Plecoptera families