Chicago hedge fund giant Citadel is closing one of its stock-focused units, Aptigon Capital, according to people familiar with the matter.

In addition, Eric Felder, who ran the unit, is leaving after less than two years at the firm. In a client letter sent Thursday, Citadel said Felder’s stock-focused portfolio managers and teams with the strongest performance and highest potential will transfer to Citadel’s other stock units.