Knights skipper Ponga was granted his wish to align with New Zealand earlier this year after previously playing with distinction for Queensland. He has not played Test football for any nation previously.
Ponga's Maori All Stars and Knights teammate Gagai has previously represented the Maroons on 23 occasions and Australia seven times, including in the 2017 World Cup final victory, but was given approval by the IRL Board last week to make the switch given his heritage and the fact he hadn't played for the Kangaroos since 2018.
Ponga was born in Australia but when he was eight his parents, with Maori heritage, moved back to Palmerston North for five years where Kalyn was a New Zealand under 13 national golf champion.
It is his desire to understand more about his culture that led to his decision to proudly play for the Kiwis.
"I definitely know who I am and the values that I have," Ponga told the World Cup website.
"That is because I am Maori and because of my mum and dad and how they brought me up.
"I think it is one thing to represent your club but another to represent a country and culture. It's special and I am still learning ... still on a journey."
The 23-man squad unveiled by Kiwis coach Stacey Jones boasts a formidable pack, captained by Warriors skipper James Fisher-Harris.
Sydney Roosters premiership-winning prop Naufahu Whyte, four-time Penrith title winner Moses Leota and Brisbane Broncos player of the year Xavier Willison headline the forward muscle.
"We're very excited for this World Cup campaign. We've been building towards this over the past few years, and winning the Pacific Championships last year was a big step in that journey," Jones said.
"I'm confident in this squad. We've got a good mix of experienced players who have been part of the team for a long time, and some new blood who all bring great talent."
There are four newcomers in the squad with Warriors powerhouses Jacob Laban and Tanner Stowers-Smith joining Gagai and Ponga.
The Kiwis take on Australia in the World Cup opener on Thursday, October 15 at Allianz Stadium.
NEW ZEALAND: Erin Clark, James Fisher-Harris, Dane Gagai, Jahrome Hughes, Jamayne Isaako, Keano Kini, Jacob Laban, Moses Leota, Jeremy Marshall-King, Te Maire Martin, Casey McLean, Ronaldo Mulitalo, Charnze Nicole-Klokstad, Briton Nikora, Kodi Nikorima, Isaiah Papali'i, Kalyn Ponga, Scott Sorensen, Tanner Stowers-Smith, Joseph Tapine, Leo Thompson, Naufahu Whyte, Xavier Willison.
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