Marx gets first crack at Bok No.2 jersey
Marx will start at hooker for South Africa when they face the Barbarians at the Wembley Stadium on Saturday – the first outing on their four-match, three-Test European venture.
Bongi Mbonambi will provide cover at hooker from the replacement bench.
Regular captain Adriaan Strauss is not in the matchday 23 and coach Alister Coetzee confirmed his absence is part of the "succession planning" in this position.
Strauss will retire from Test rugby after the tour – which also features Tests against England (London, November 12), Italy (Florence, November 19) and Wales (Cardiff, November 26).
"We rewarded several young players for their performances in Super Rugby and the Currie Cup ," Coetzee said, adding that they will approach this match as a Test – although no caps will be awarded.
"It will be a really big occasion for our young players, but we're excited to be giving them an opportunity," the coach said.
Marx has just one cap – coming off the bench in a lost cause against the All Blacks in a Rugby Championship match in Christchurch in September – a game the Boks lost 13-41.
Marx got the call-up after he delivered some impressive performances for the Lions in the 2016 Super Rugby competition.
The 22-year-old also represented the Junior Springboks at the 2014 World Under-20 Championships.
Mbonambi has made three appearances for the Boks, all off the bench.
The 25-year-old made his debut against Ireland in Port Elizabeth in June – a game South African won 19-13 with a late rally, to clinch the series 2-1.
His last Test was another lost cause, the humiliating 15-57 record loss to the All Blacks in Durban last month.
Mbonambi has seen a change of playing fortunes since he moved from Pretoria to Cape Town, where he won the Most Promising DHL Western Province Forward award in 2015.
He is powerfully built and has a huge on-field work-rate.
Coetzee said the BaaBaas – featuring six South African players – will pose a huge threat to the Boks.
"The Barbarians play an attacking, adventurous style of rugby and it will be a real test for our young side," said Coetzee.
"They have an excellent, world-renowned coach in Robbie Deans, exciting young players in their side, including some South Africans, as well as several players who have a lot of Test match experience.
"Even though some of the experienced players were last in action against New Zealand four weeks ago, our preparation the past few weeks was really good.
"The excitement and enthusiasm of the new inclusions are contagious. In ideal circumstances, I would've preferred to give every player in the squad a run, but this tour was also about introducing players who are on our radar for the future, while also introducing them to the Springbok way and ethos. I am sure they will work even harder to stay in the squad."
