Oh, yes, these are the only and I bet most mysterious gibbons in Brazil

it's weird because when you search for them in google, you won't find any articles or news about them; I only know they exist because i've seen them personaly in 2018, but for incredible (or weird) that it seems, there's no information sign on their exhibit, so I was lucky that I knew what they were, otherwise I'd just confuse them with spider monkeys as most of the people do (their exhibit is right next to the spider monkeys, and these others actually have an information sign on their enclosure

)
This issue of the sign unfortunately doesn't look temporary, once, when an uncle of mine went to Goiânia zoo a few months after I did, i asked him to observe if there was an information sign already, and he said there wasn't... Anyway, the zoo is now passing through a renovation, and I hope they improve this and other aspects on their Siamang gibbon keeping.
Now talking abou how long they have been there and their origin; this is probably the topic that I have less knowledge about these animals... I cannot even imagine where these two came from, nor how long they have been there (they're there at least since 2012, cause I''ve seen a video in youtube showing them in this date), but I'm gonna try to ask the zoo directly in their social media, and see if they answer me. Once I still don't know a lot about these gibbons, I'll do another post in this thread to tell what I've found out.
In case somebody wants to see how their enclosure looks like, I'll let the links of some videos I recorded in my last visit to zoo Goiânia:
20180128101611.MTS
20180128101828.MTS
20180128101704.MTS