Gorillas? Cos I think they partner up for life... and actually, 50% of their children have a different father. So their "monogamy" is more of a partnerhood rather than only-mates-for-life... Just a guess
I was thinking it is clown fish too .. but it cant ( well i don't think so anyway). there is one female and males.. if the female dies the main male becomes female. there are two females in the picture.