MTG: Ixidron vs Morph
The text printed on the Ixidron reads as follows:


  As Ixidron enters the battlefield, turn all other nontoken creatures
  face down. (They're 2/2 creatures.) Ixidron's power and toughness are
  each equal to the number of face-down creatures on the battlefield.


As morphed creatures are already face-down they are unaffected.
This is reflected in the Ruling made in 2006:


  2006-09-25 : Turning a face-down creature face-down typically has no effect; the creature’s status is unchanged.