Munster's Jean Kleyn and Mike Haley are the two uncapped names in Ireland's squad to prepare for the World Cup, the Irish Rugby Football Union announced on Tuesday.
South Africa born lock Kleyn, 25, qualifies for his new country on August 8 having spent three years there, while full-back Haley, 24, grew up in England but has an Irish grandmother.
Injured Leinster back-rowers Dan Leavy and Sean O'Brien miss out.
Hooker Rory Best, who led his country during this year's Six Nations is the most experienced player on the list with 117 international appearances and will retire after the tournament which begins on September 20.
Joe Schmidt's side's World Cup campaign starts by facing Scotland before playing hosts Japan, Russian and Samoa in Pool A.
Preliminary Ireland squad for Rugby World Cup
Finlay Bealham, Rory Best, Tadhg Beirne, Jack Conan, Sean Cronin, Ultan Dillane, Tadhg Furlong, Cian Healy, Iain Henderson, Rob Herring, Dave Kilcoyne, Jean Kleyn, Jack McGrath, Jordi Murphy, Tommy O'Donnell, Peter O'Mahony, Andrew Porter, Rhys Ruddock, James Ryan, John Ryan, Niall Scannell, CJ Stander, Devin Toner, Josh van der Flier
Bundee Aki, Ross Byrne, Joey Carbery, Jack Carty, Andrew Conway, John Cooney, Keith Earls, Chris Farrell, Mike Haley, Robbie Henshaw, Dave Kearney, Rob Kearney, Jordan Larmour, Kieran Marmion, Luke McGrath, Conor Murray, Garry Ringrose, Rory Scannell, Jonathan Sexton, Jacob Stockdale