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The epigyne or epigynum is the external genital structure of female
An example of a comparatively simple epigyne is that of '' Pirata montanus''. 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'', where the lateral expansions often conceal the openings of the spermathecae, as in the epigyne of '' Geolycosa pikei''.
A more complicated form of epigyne is found in spiders of the genus '' Araneus'', 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 (
File:Paraphidippus aurantius epigyne.jpg, '' Paraphidippus aurantius''
File:Hakka himeshimensis epigyne.jpg, '' Hakka himeshimensis''
File:Thiodina puepera epigyne.jpg, '' Colonus puerperus''
File:Hentzia chekika epigyne.jpg, '' Hentzia chekika''
File:Sparassidae sp. 1 (epigynum).jpg, '' Isopeda'' sp., probably '' Isopeda villosa''
The epigyne or epigynum is the external genital structure of female spider
Spiders (order (biology), order Araneae) are air-breathing arthropods that have eight limbs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude spider silk, silk. They are the largest order of arachnids and ran ...
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 () . is a skeleton that is on the exterior of an animal in the form of hardened integument, which both supports the body's shape and protects the internal organs, in contrast to an internal endoskeleton (e.g. human skeleton, that ...
located on the underside of the abdomen, in front of the epigastric furrow 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 thespermatheca
The spermatheca (pronounced : spermathecae ), also called ''receptaculum seminis'' (: ''receptacula seminis''), is an organ of the female reproductive tract in insects, e.g. ants, bees, some molluscs, Oligochaeta worms and certain other in ...
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 typica ...
.
Differences in form
An example of a comparatively simple epigyne is that of '' Pirata montanus''. 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'', where the lateral expansions often conceal the openings of the spermathecae, as in the epigyne of '' Geolycosa pikei''.
A more complicated form of epigyne is found in spiders of the genus '' Araneus'', 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 Portugal) is a family of very small spiders comprising 4706 described species in 6 ...
) and orb weavers ( Araneidae), 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.
References
External links
* {{Spider nav Sex organs Spider anatomy