Board Thread:Questions and Answers/@comment-26848457-20150802191529/@comment-26841482-20150821151120

Uta's kagune is CHAIR-SAMAAA!!! His kagune was the only thing that could control Aizen's powers

Jokes aside, as Harostar said, Uta's kagune has never been shown or discussed. It's like he's compensating for not showing his kagune by always showing his kakugan. But, personally I would say that he's a koukaku.