It says a lot about the strength in depth of the Ireland squad that Tom Tierney can leave a former World Player of the Year nominee on the bench.
Sophie Spence had problems with concussion last season but her timely return during the Six Nations was seen as a major boost to Ireland's chances of winning a home World Cup.
But the powerful second-row has to make do with an impact role for now at least as Tierney shuffles his pack and brings Ulster's Ashleigh Baxter, a former winger, into the back-row, while regular No.8 Paula Fitzpatrick switches to the engine room in place of Spence.
In recent years, Spence and Marie-Louise Reilly's second-row partnership was one of the bedrocks on which Ireland's game-plan was based but this is a new-look pack.
Reilly said: "I think it shows the progression of our team in the last couple of years that we have got strength in depth now - everyone is fighting for their place.
"Baxter can come in, she's a formidable rucker so flanker is going to suit her down to the ground. And then Paula Fitz is just so talented. She can really play in any position. She would have played 10 for her club before so she's more than capable of playing that role. We've got a huge bench coming in then so it's going to be a formidable team."
Ireland's set-piece is generally very strong and against an Australian outfit largely made up of Sevens specialists looking to thrive on broken play, Reilly knows that her side's scrum and lineout are crucial to getting off to a winning start.
"As ever, a game can really swing with your set-piece," the Leinster lock added. "We pride ourselves on our scrum and lineout ability. We will look to try and gain an advantage there.
"They have a lot of talent with the Sevens players. We too have Sevens players coming in. We are on an even keel in that regard.
"For us, it is just another team. We do our analysis to find their strengths and weaknesses and plan our game around that."
England will showcase enviable squad depth when they kick off the tournament against Spain today. Head coach Simon Middleton has named 12 World Cup newcomers in the match-day 23, while the replacements' bench features a combined total of 392 caps as England set out on the defence of a title they won in France three years ago.
Italy and the United States complete England's pool, and they should get off to a flying start at Dublin's UCD Bowl.
Wales will launch their campaign against a team head coach Rowland Phillips describes as one of the "perennial favourites".
Phillips' squad have arrived in Dublin following a poor Six Nations campaign, and they find themselves facing a Herculean challenge in four-time World champions New Zealand.
With 2014 World Cup runners-up Canada also in their pool, it is a group that will test Wales, but Phillips said: "A lot has been said about the pool we are in. We know we have a huge challenge in front of us."