The flatfish life-style or 'habit' evolved several times independently, and so the group is polyphyletic. Their young are perfectly symmetrical, but the head is remodelled during a metamorphosis. One eye moves to the other side, close to the other eye. Some species have both eyes on the left (turbot), some on the right (halibut, sole); all living and most fossil flatfish to date show an 'eyed' side and a 'blind' side.