Intriguingly Louise Rickard, who with in excess of 100 internationals as a winger or full-back, and who is the world's record cap holder, is one of those battling for a coveted place - but as a second row.
Explaining his decision, Lewis said: "Lou and I have spoken. Competition in the back three has grown steadily over the last year or so. She still remains a very good rugby player. It's just about where in the team can she be accommodated, if at all.
"She's always been a very fit individual. She has the mental fitness without question, she is very powerful, but can she jump? We need to find out and if she can she could find a place in the second row."
On leaving three places open, he said: "The thought process behind that is that we think there are 23 definites who showed through their performances recently they are worthy of their place.
"There are seven players who have to continue to show us they are worthy of a place - so it's up to those players to put their hands up to gain one of the three places."
In a squad which Lewis says is a balance of youth and experience, he has selected six players from the Wales Under 20 squad with another - full back Kerin Lake - on the list of possibles.
Hooker Lowri Harries, prop Alex Stokes, second row Shona Powell-Hughes and Sioned Harries and backs Mared Evans (fly-half or full back) and centre Adi Taviner have taken their chances to impress the Welsh selection panel in a bid to force their way in.
"We've watched a number of girls in the two recent U20 internationals against England. They've also played in the recent regional selections and stood out, confirming in my mind they can play at senior level and make a difference. The girls we've selected add value to the squad and hopefully they can go on to be the future of the squad," he added.
Berry's move to the midfield from the back row may also raise a few eye brows but Lewis has no doubt the inspirational No8 can adapt to her new surroundings.
"Mel's been captain for something like five years. There is nothing wrong in her captaincy but we've moved her to the centre and she's going to have plenty to think about there so we're hoping to lighten the workload in what will be an intensive month. Therefore we've picked a second captain and Jamie Kift is that person."
Wales will face Australia, South Africa and New Zealand in the Group of Death and must finish top if they are to qualify for the semi-finals - a task some would suggest is extremely difficult.
"We'll be underdogs but I am comfortable with that, there is no easy side in that pool," said Lewis. "We've got to go out and win our games against Australia and South Africa to be in with a chance. Then it's down to the last game against New Zealand - I am confident we can go out and put in a good performance."
Wales Women's World Cup squad:
Forwards: Jenny Davies Waterloo/ Blues, Lowri Harries UWIC/ Blues, Catrin Edwards Cardiff Quins/ Scarlets, Alex Stokes Neath Athletic/ Ospreys, Rhian Bowden UWIC/ Dragons, Gemma Hallett Pontyclun/ Blues, Shona Powell-Hughes Neath Athletic/ Ospreys, Rachel Taylor Cardiff Quins/ Ospreys, Catrina Nicholas Cardiff Quins/ Blues, Jamie Kift (captain) Bristol Ladies/ Dragons, Sioned Harries UWIC/ Scarlets, Lisa Newton UWIC/ Ospreys.
Backs: Amy Day Bristol Ladies/ Dragons, Laura Prosser Cardiff Quins/ Blues, Awen Thomas Unattached/ Scarlets, Naomi Thomas Cardiff Quins/ Scarlets, Mared Evans UWIC/ Dragons, Claire Flowers Bristol Ladies/N/A , Ceri Redman UWIC/ N/A, Mellissa Berry (captain) Blaydon/ N/A, Caryl James Cardiff Quins/ Scarlets, Non Evans Cardiff Quins/ Scarlets, Adi Taverner Neath/Ospreys.
Possibles (three to be selected) from: Hannah Roberts (prop) UWIC/Dragons, Louise Rickard (second row) Woodbridge/ N/A, Caryl Thomas (prop) Bath Ladies/ Dragons, Kerin Lake (full back) Neath Athletic/ Ospreys, Kay Rees (centre) Harlequins/ Dragons, Elen Evans (centre) Dolgellau/ Scarlets, Elinor Snowsill (Back) Loughbourgh/ N/A.