these are Elpidium, ostracods (seed shrimp!) which only live in the water that collects between the leaves of bromeliad plants. that's it. to reach new plants, they stick themselves onto other animals, including frogs, and ride around passively.

I got a question off site asking how big this little friend was. I just realized the crop doesn't show how absolutely tiny it was.

3rd photo is uncropped straight from my camera, it was basically the smallest thing my lens could capture.