Some flatworms, for instance these pretty Pseudobiceros hancockanus, engage in penis fencing. Both individuals are hermaphrodites, i.e., have both male and female organs. The penis is white, pointed and two-headed. Both individuals are trying to inseminate the other. The one who is inseminated has to bear and lay eggs - a more expensive proposition. The one who "won" the fencing bout and did the insemination can move on and fence some other guys and on and on, "fathering" many progeny until happenning onto a better fencer, getting inseminated, and spending the rest of the life as "mother".
for real, 'hancockanus'? it strains one's capacity for belief...
why oh why is there not a video?
I wonder how that behaviour would combine with the morphology of the New Zealand multivirile flatworm - 220 odd penises either side would make for some interesting fights
Yup, scientists have a sense of humor and often use it when naming species.
David, thank you - that one goes into my folder of ideas for future installments of Friday Weird Sex Blogging.