Tony McGahan's extended squad for the 2011/12 Heineken Cup also includes recent signings Ian Keatley, BJ Botha and Will Chambers and Development prop John Ryan.
Notable absentees are Jerry Flannery, David Wallace and Felix Jones, who were all ruled out by the injuries they sustained while preparing for or participating in the Rugby World Cup.
Due to injuries in the front row, veteran prop John Hayes has been included for the pool stages of the tournament.
Darragh Hurley and Peter Borlase, both of whom are expected to resume full training in the coming weeks, could join the squad after rounds 1 and 2 under ERC regulations as is the case with Flannery.
Meanwhile, 21-year-old Youghal native O'Callaghan, who plays his club rugby for Dolphin, has been selected after making his first competitive start for Munster against the Ospreys earlier this month.
Other newcomers, front rower Ryan from Cork Constitution and UL Bohemians hooker Henry, are both 23.
Henry won three provincial caps as a replacement last season, while Ryan recently made his first two senior appearances off the bench against the Cardiff Blues and Edinburgh in the RaboDirect PRO12.
MUNSTER Heineken Cup Squad - Backs (16): Scott Deasy, Doug Howlett, Denis Hurley, Johne Murphy, Simon Zebo, Danny Barnes, Will Chambers, Tom Gleeson, Keith Earls, Lifeimi Mafi, Ronan O'Gara, Ian Keatley, Tomas O'Leary, Conor Murray, Duncan Williams, Peter Stringer.
Forwards (22): Denis Fogarty, Damien Varley, Mike Sherry, Sean Henry, Marcus Horan, John Hayes, Stephen Archer, Wian du Preez, BJ Botha, John Ryan, Paul O'Connell, Donncha O'Callaghan, Mick O'Driscoll, Ian Nagle, Donnacha Ryan, Niall Ronan, Billy Holland, Tommy O'Donnell, Peter O'Mahony, David O'Callaghan, Denis Leamy, James Coughlan.