In Truk Lagoon, Micronesia I found this nudibranch mating.
Nudibranchs are hermaphroditic (both male and female organs), functioning
first as a male while the female organs mature. Some advance
members have three sexual ducts; One for outgoing sperm, one for outgoing eggs,
and one for incoming sperm.
Many colors and shapes (click HERE for more pictures).
click on pictures for larger versions