Hi! welcome to the forum. There are three species of frogs that I know of named after German anatomist, Johannes Mueller:
Xenopus muelleri (Mueller's Platanna/Geelpensplatanna)
Dermatonotus muelleri (Pudgy Frog)
Centrolene muelleri
If you have a picture or description, we may be able to help. I also worked at a zoo as an amphibian keeper.