Capniidae
Encyclopedia
Capniidae, the small winter stoneflies, is a family
of insect
s in the stonefly order
(Plecoptera). It constitutes one of the largest stonefly families, containing some 300 species
distributed throughout the Holarctic
. Their closest relatives are the rolled-winged stoneflies (Leuctridae).
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). Indeed, some wingless Capniidae – e.g. the Lake Tahoe Benthic Stonefly ("Capnia" lacustra) or Baikaloperla spp. – spend their entire life cycle
underwater and do not disperse from their native lakes at all.
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.
Nymph
s 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
.
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 clade
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.
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 America
n 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
Suspected clade/subfamily 1
Suspected clade 2/subfamily Capniinae sensu stricto Allocapnia
Baikaloperla
Capnia (paraphyletic)
Capnura
Utacapnia
Mesocapnia
Incertae sedis
as to clade 1 or 2
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s in the stonefly order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
(Plecoptera). It constitutes one of the largest stonefly families, containing some 300 species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
distributed throughout the Holarctic
Holarctic
The Holarctic ecozone refers to the habitats found throughout the northern continents of the world as a whole. This region is divided into the Palearctic, consisting of Northern Africa and all of Eurasia, with the exception of Southeast Asia and the Indian subcontinent, and the Nearctic,...
. Their closest relatives are the rolled-winged stoneflies (Leuctridae).
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). Indeed, some wingless Capniidae – e.g. the Lake Tahoe Benthic Stonefly ("Capnia" lacustra) or Baikaloperla spp. – spend their entire life cycle
Biological life cycle
A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...
underwater and do not disperse from their native lakes at all.
Description and ecology
Adult Capniidae, as their common name implies, 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 25 mm (1 inch) at adulthood. The adults emerge from the water in winter and are often found walking around on the snow. Characteristic are the wingsInsect wing
Insects are the only group of invertebrates known to have evolved flight. Insects possess some remarkable flight characteristics and abilities, still far superior to attempts by humans to replicate their capabilities. Even our understanding of the aerodynamics of flexible, flapping wings and how...
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.
Nymph
Nymph (biology)
In biology, a nymph is the immature form of some invertebrates, particularly insects, which undergoes gradual metamorphosis before reaching its adult stage. Unlike a typical larva, a nymph's overall form already resembles that of the adult. In addition, while a nymph moults it never enters a...
s 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
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
, from segment 1 to 9, is generally very pronounced.
The nymphs dwell in the hyporheic zone, the interface between stream water and groundwater
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...
. Only immediately before moulting
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
into the adult form will the nymphs move out of the substrate and appear on the stream bed
Stream bed
A stream bed is the channel bottom of a stream, river or creek; the physical confine of the normal water flow. The lateral confines or channel margins, during all but flood stage, are known as the stream banks or river banks. In fact, a flood occurs when a stream overflows its banks and flows onto...
. Thus, although they may be plentiful in clean rivers and streams, they are seldom encountered in standard samples of benthos
Benthos
Benthos is the community of organisms which live on, in, or near the seabed, also known as the benthic zone. This community lives in or near marine sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths.Many organisms...
.
Systematics and taxonomy
The family Capniidae is often considered to be monotypicMonotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
as to subfamily, with the Capniinae being inserted at that rank. However, this is rather pointless; in any case the phylogeny, systematics
Systematics
Biological systematics is the study of the diversification of terrestrial life, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees...
and taxonomy
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
of the small winter stoneflies are highly confused. There appear to be two very basal genera and presumably two larger clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
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.
Furthermore, the type genus
Type genus
In biological classification, a type genus is a representative genus, as with regard to a biological family. The term and concept is used much more often and much more formally in zoology than it is in botany, and the definition is dependent on the nomenclatural Code that applies:* In zoological...
Capnia is probably not monophyletic and in serious need of splitting up. The type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
Capnia nigra and its closest relatives would retain their genus name; they are closely related to Capnura. The North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
n 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
Incertae sedis
Incertae sedis
, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...
as to clade 1 or 2
- Allocapniella
- Capniella
- Capnopsis
- Eocapnia
- Takagripopteryx
- Some species presently in Capnia