BANGKOK (Reuters) - Thailand's Bank of Ayudhya Pcl (BAY) announced in a filing on Thursday it would acquire Nomrua's securities unit in Thailand for $155.3 million.    Japan's Mitsubishi UFJ Financial Group holds a 76.9% stake in Bank of Ayudhya, Thailand's fifth largest bank by assets. The transaction is subject to approval from the Thai central bank, BAY said.    

(Reporting by Chayut Setboonsarng and Makiko Yamazaki in Tokyo; Editing by Martin Petty)