epigyne

noun

1. The external female sex organ in arachnids.

   “1996: This [genital] area is inconspicuous in most adult males and in immature females, but in adult females of the majority of species it is modified into a variably shaped, more or less sclerotized structure called the epigyne. — Michael J. Roberts, Spiders of Britain and Northern Europe (Collins 1996, p. 16)”