Is there a special name for a contributed talk given longer time slot?
This sounds like a fairly unusual format; I don't think there is a standard name for it that would be recognizable.

If you want to highlight your contribution you could always add some extra description of the content of some sort. 

In this case the length of your talk might set it apart, as it implies a bigger contribution to the conference and shows you have experience in doing more than just the typical brief talk:


  "Sproingity Sproing", International Symposium on Blahdy Blah, March 2017. (40 minute oral presentation).