NEW YORK, Jan. 27, 2012 /PRNewswire/ -- Momenta Pharmaceuticals, Inc. (NASD: MNTA) will replace HealthSpring, Inc. (NYSE: HS) in the S&P SmallCap 600 index after the close of trading on Tuesday, January 31. S&P 500 constituent Cigna Corp. (NYSE: CI) is acquiring HealthSpring in a deal expected to be completed on January 30, pending final approvals.

Momenta Pharmaceuticals is a biotechnology company specializing in the characterization and process engineering of complex molecules. Headquartered in Cambridge, MA, the company will be added to the S&P SmallCap 600 GICS (Global Industry Classification Standard) Biotechnology Sub-Industry index.

Following is a summary of the change:

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