Tamarin
There is a successful breeding colony of these tiny monkeys here in a zoo in New Plymouth.
It is possible for humans to enter their tree-filled cage so that there is nothing between the tamarin and the human observer. I'm interested in doing a serious portrait of one, but so far this is as good as I have been able to manage. I've been back many times with my camera but still have not managed to improve on this. The zoo is a few minutes walk from my home, and it's a council run, free entry zoo so I will keep trying. There are some photos eg portraits of tadpoles, that I have been working on for many years. I would also like to do a portrait of a slug.