Ciena (CIEN), a S&P MidCap 400 constituent, will replace Dayforce (DAY) in the S&P 500 index on Feb. 9, following the acquisition of Dayforce by Thoma Bravo, S&P Dow Jones Indices said Wednesday.

Arrowhead Pharmaceuticals (ARWR) will replace Ciena in the S&P MidCap 400, and ADT (ADT) will replace Arrowhead in the S&P SmallCap 600, it added.