Epigynum

Definition

The external, sclerotized genital plate of female spiders (Araneae), located on the ventral surface of the opisthosoma (abdomen) anterior to the epigastric furrow and the book lungs. The epigynum contains the copulatory openings that lead via insemination ducts to the spermathecae, and typically features species-specific grooves, pockets, or projections that guide male pedipalps during mating. Its intricate, often diagnostic morphology is the primary basis for species identification in many spider families, particularly when examined via microscopy or micro-CT.

Etymology

From Greek epi- (upon, above) + gynē (woman, female), referring to its position on the female body.

Example

In wolf spiders (Lycosidae), the epigynum bears a median septum flanked by copulatory openings; males use their palpal bulbs to align with these structures, and subtle differences in septum shape distinguish otherwise similar species such as Hogna carolinensis from H. helluo.

Synonyms

• epigyne

Related Terms

• spermatheca
• pedipalp
• opisthosoma
• epigastric furrow
• book lung
• insemination duct
• copulatory opening
• Spinneret

Usage Notes

The term is strictly arachnological; it does not apply to insects, which have internal genitalia (bursa copulatrix, spermatheca) without a comparable external sclerotized plate. Some arachnologists use 'epigyne' as a variant spelling, but 'epigynum' remains standard in taxonomic literature. The epigynum is often partially or fully concealed by hairs or cuticular folds in live specimens, requiring clearing or dissection for definitive study. Do not confuse with the plant genus Epigynum (Apocynaceae).