No doubt about it. It's fungus. Get it clean if you want to keep using the lens as it will over time spread further. For now I doubt you notice anything or just a little depending on the F-stop when you examine photos shot with this lens. Because it starts in the side moving to the center that is better then one that starts in the middle heh.. Fungus can eat and damage your element's coating. It that happens that uncoated area can yield slight color change.
I have seen fungus for a few decades, I am sure that is a fungus. heh. That lens is really dirty too from the look of the specks...Bring back to canon to clean or someone who does this privately. I think there is someone here who can do that.. his name is thrown around here a lot.. you can find it in the Nikon thread link http://www.clubsnap.com/forums/showthread.php?t=1548492
When buy second hand got this problem. Problem bigger when its online you cant inspect. After that you LL and when they play the ship back the stupid item trick, you incur shipping costs. End of the day, suck thumb. Get partial refund is the better route.