The epigyne or epigynum is the external genital structure of female

spider Spiders ( order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...

s. As the epigyne varies greatly in form in different species, even in closely related ones, it often provides the most distinctive characteristic for recognizing species. It consists of a small, hardened portion of the

exoskeleton An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton (endoskeleton) in for example, a human. In usage, some of the ...

located on the underside of the abdomen, in front of the

epigastric furrow The anatomy of spiders includes many characteristics shared with other arachnids. These characteristics include bodies divided into two tagmata (sections or segments), eight jointed legs, no wings or antennae, the presence of chelicerae and pedi ...

and between the epigastric plates.

Functions

The primary function of the epigyne is to receive and direct the palpal organ of the male during copulation. The various specific forms of epigynes are correlated, in each case, with corresponding specific differences in the palpus of the male. This specialization prevents individuals of different species from mating. The epigyne covers or accompanies the openings of the

spermatheca The spermatheca (pronounced plural: spermathecae ), also called receptaculum seminis (plural: receptacula seminis), is an organ of the female reproductive tract in insects, e.g. ants, bees, some molluscs, oligochaeta worms and certain other ...

e, which are pouches for receiving and retaining sperm. Frequently, the openings of the spermathecae are on the outer face of the epigyne and can be easily seen. A secondary function of the epigyne is as an

ovipositor The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typical ...

Differences in form

An example of a comparatively simple epigyne is that of ''

Pirata montanus ''Pirata montanus'' is a species of wolf spider from the family Lycosidae Wolf spiders are members of the family Lycosidae (). They are robust and agile hunters with excellent eyesight. They live mostly in solitude, hunt alone, and do not spin ...

''. It consists of a nearly plain plate, with the openings of the spermathacae near the posterior lateral corners. A somewhat more complicated form is illustrated by the epigyne of '' Trabeops aurantiacus''. In this species, the plate is depressed or furrowed longitudinally, and the depressed area is divided by a ridge-like elevation, which divides the depression into two furrows or channels, each of which leads to the opening of the spermatheca of the corresponding side. This ridge-like elevation is called the ''guide'', as its function "seems clearly to be that of a guide to the male embolus, controlling the course of the latter and facilitating its entrance to the spermatheca." In many cases the guide extends laterally on each side at its posterior end. This is true to a slight extent in the epigyne of '' Trabeops'', but more markedly so in that of many species of ''

Geolycosa ''Geolycosa'' is a genus of wolf spiders first described in 1904. Species , it contains 75 species: *'' Geolycosa aballicola'' (Strand, 1906) *'' Geolycosa albimarginata'' (Badcock, 1932) *'' Geolycosa appetens'' Roewer, 1960 *'' Geolycosa ash ...

'', where the lateral expansions often conceal the openings of the spermathecae, as in the epigyne of ''

Geolycosa pikei ''Geolycosa pikei'' is a species of wolf spider in the family Lycosidae from the United States. It can blend into sand, which it also burrows in. The spider can heal its wounds quickly. Description The spider is sandy gray to brown with black ma ...

''. A more complicated form of epigyne is found in spiders of the genus ''

Araneus ''Araneus'' is a genus of common orb-weaving spiders. It includes about 650 species, among which are the European garden spider and the barn spider. The genus was erected by Carl Alexander Clerck in 1757. Description Spiders of this genus prese ...

'', where there is developed an appendage which is usually soft and flexible, and which is termed the ''scape'' or ''ovipositor''. When there is a well-developed scape, the tip of it is usually more or less spoon-shaped. This part of the scape is termed the ''cochlear''. The basal plate of the epigyne which bears the scape, and which forms a porch or hood that covers the opening of the oviduct is called the ''atriolum''. A still more complicated form of epigyne is found in some of the sheet weavers (

Linyphiidae Linyphiidae, spiders commonly known as sheet weavers (from the shape of their webs), or money spiders (in the United Kingdom, Ireland, Australia, New Zealand, and in Portugal, from the superstition that if such a spider is seen running on you, ...

) and orb weavers (

Araneidae Orb-weaver spiders are members of the spider family Araneidae. They are the most common group of builders of spiral wheel-shaped webs often found in gardens, fields, and forests. The English word "orb" can mean "circular", hence the English name ...

), where the ovipositor consists of two finger-like projections: first, the more common one, the scape, which arises from the atriolum, and consequently in front of the opening of the oviduct; and second, one which arises behind the opening of the oviduct; this is termed the ''parmula''. Each of these projections may be grooved on the side facing the oviduct, forming a tube. File:Thiodina sylvana epigyne.jpg, '' Colonus sylvanus'' File:Theridula emertoni epigyne.jpg, '' Theridula emertoni'' File:Thiodina puepera epigyne.jpg, '' Colonus puerperus'' File:Phidippus clarus epigyne 01.jpg, '' Phidippus clarus'' File:Sparassidae sp. 1 (epigynum).jpg, '' Isopeda'' sp., probably '' Isopeda villosa'' File:Araneus diadematus epigyne (D19-101-148a).jpg, ''

Araneus diadematus The spider species ''Araneus diadematus'' is commonly called the European garden spider, diadem spider, orangie, cross spider, and crowned orb weaver. It is sometimes called the pumpkin spider, although this name is also used for a different spec ...

References

External links

* {{Spider nav Sex organs Spider anatomy