Financial terms of the deal, announced Tuesday, weren't revealed.
The 23-year-old Galiardi played only 35 games last season because of wrist and forearm injuries. He finished with seven goals and eight assists. The Avalanche selected Galiardi in the second round of the 2007 draft.
Rissmiller, 32, played for five teams last season, including the Lake Erie of the American Hockey League. He was originally signed by the San Jose Sharks in June 2003 and has played in 192 NHL games.
Unless he really collapses, I don't see him going anywhere. I've been very impressed with his composure and maturity. Once the regular season started, he was a different guy; it was like game on and almost as if he's been around for a long time.
— Florida Panthers general manager Dale Tallon on rookie defenseman Aaron Ekblad