It seems our friends over at the Dechronization blog have discovered that the internet was made for porn.
I will not be outdone. Herewith, a pair of Chtonobdella (c.f.) bilineata in-copulo! (Credit to Ralph Davis of Sydney, Australia).
Leeches are hermaphrodites, and most of these terrestrial jungle leeches have their male and female gonopores separated by 5 or fewer annuli. The male gonopore from which the penis is pushed out, is anterior to the female gonopore and the vagina; hence the head-to-tail (69) copulation technique. In fact, internal fertilization, though also a characteristic of aquatic medicinal leeches, seems to have originated in their terrestrial ancestors as a way to avoid sperm dessication.
So there... "porn", "penis", "vagina", "69", "sperm" and "copulation" all in one post.