No, not by race number; then all the 9 Discovery riders would start last.

The pack is divided into 9 groups, and the team managers have to nominate 1 rider for each group. Within the groups, I guess, they can start acc. their race number.
Normally (and this could be mandatory) #1 starts as the last rider in the last group. And #11 (this is usually the number for the 2nd on the podium from last year) as the 2nd last rider? This can be a disadvantage if it's forseeable that the weatherconditions will be worse till the end. Then, for example, Riis could nominate Basso for the first group.