Andrew Trimble has been omitted from Ireland's World Cup squad, with boss Joe Schmidt gambling on selecting just two scrum-halves.
Head coach Schmidt has taken the calculated risk of only picking Conor Murray and Eoin Reddan at scrum-half, to make room for an extra centre in Ulster's Darren Cave.
Isaac Boss and Kieran Marmion miss out as a result, with props Nathan White and Tadhg Furlong both included as expected.
"The players have worked incredibly hard over the past two months," said coach Schmidt.
"Sunday was a difficult and very long day for the coaching team and an anxious one for many players.
"There were some very tight decisions, particularly in the back-three and it was also challenging to make sure that key positions were covered as much as a squad of 31 players allows.
"A number of players were very unlucky to miss selection.
"We know from observing past World Cups that it's important for us to keep track of their performances because some of them are likely to be involved in the tournament."
Ireland face England at Twickenham on Saturday in their final World Cup warm-up clash, before opening their Pool D campaign against Canada in Cardiff on September 19.
Loosehead prop Cian Healy is included despite his continued fight to recover from neck surgery in May, while Leinster tighthead Marty Moore misses out owing to foot trouble.
There is no place for veteran centre Gordon D'Arcy, whose glittering Test career looks over barring injury, after 16 years and 82 caps.
Munster flyer Keith Earls gets the nod despite suffering a worrying blow in Saturday's 16-10 Dublin defeat to Wales.
Kiwi boss Schmidt's biggest call has come in dispensing with the services of a third scrum-half however, a move that carries inherent risk given the highly-specialist nature of the position.
Without the World Cup being hosted in England and that proximity to home, Schmidt would have been hard-pressed for such luxuries.
Ireland will be able to draft in either Boss or Marmion quickly and easily should injury demand - but any last-minute problem could leave Schmidt's men short on match-day.
In that scenario it seems Leinster fly-half Ian Madigan would cover scrum-half from the bench.
New Zealand-born prop White became Ireland's third-oldest debutant of all time last month, and has impressed suitably to earn himself a spot in Ireland's final 31-man squad.
Fast-developing Leinster prop Furlong only made his Test debut against Wales at the weekend, and now finds himself thrust into a World Cup party.
The 22-year-old did enough in Dublin at the weekend to dislodge Michael Bent, whose versatility in covering both sides of the scrum had given him a perceived selection advantage.
Lock Paul O'Connell captains the squad, fresh from his final Aviva Premiership appearance in Ireland colours against Wales.
The 35-year-old will retire from the Test arena after the tournament, and swap home province Munster for European aristocrats Toulon.
Munster lock Donnacha Ryan has edged out Ulster's Dan Tuohy in the second row, the 31-year-old finally able to prove his fitness this summer and end 29 months without Test rugby.
Ireland's squad for the 2015 World Cup:
Props: T Furlong, C Healy, J McGrath, M Ross (all Leinster), N White (Connacht)
Hookers: R Best (Ulster), S Cronin, R Strauss (both Leinster)
Locks: I Henderson (Ulster), P O'Connell (Toulon, captain), D Ryan (Munster), D Toner (Leinster)
Back-row: J Heaslip (Leinster), C Henry (Ulster), J Murphy, S O'Brien (both Leinster), P O'Mahony (Munster)
Scrum-halves: C Murray (Munster), E Reddan (Leinster)
Fly-halves: P Jackson (Ulster), I Madigan, J Sexton (both Leinster)
Centres: D Cave (Ulster), K Earls (Munster), L Fitzgerald (Leinster), R Henshaw (Connacht), J Payne (Ulster)
Back three: T Bowe (Ulster), D Kearney, R Kearney (both Leinster), S Zebo (Munster)