Semanufagai arrived in May to help the club’s bid to fight off the threat of relegation but fellow Cronualla front-row Prior has now joined him at Leeds for 2020.
A New South Wales State of Origin representative, Prior boasts plenty of talent and grit is certainly set to help strengthen Rhinos’ pack.
He won a Grand Final with Cronulla - and also St George-Illawarra - and was in the same squad for 18 months alongside Seumanufagai at Sharks before the latter made the switch to Super League.
Seumanufagai said: “He brings a lot of experience; he’s played over 200 games and won two Grand Finals.
“I’m looking forward to playing with him. I think we complement each other.
“He’s a very, very good defender and a good runner of the ball.
“He’s got a great engine, too, and we’re pretty familiar with each other’s style.”
At 32, Prior has built up plenty of experience in the sport and the New Zealander conceded: “I think he’ll bring a lot.
“He’ll help us a lot in the middle in terms of defence and teaching some of the younger boys some of the ropes.”
Leeds have confirmed the rest of their squad numbers for 2020 and - if they are anything to go by - the former Cronulla duo are set to be starting props.
Seumanufagai has been rewarded for his efforts in the second half of last season by being promoted to the No 8 jersey and Prior takes the No 10 shirt vacated by Brad Singleton’s recent move to Toronto Wolfpack.
With veteran Australian Adam Cutbertson and double Super League Grand Final winner Dom Crosby also in the ranks as well as England Knights Mikolaj Oledzki and England Academy duo Muizz Mustapha and Tom Holroyd, head coach Richard Agar now has plenty of front-row options.
Seumanufagai, 28, is enjoying getting his first full pre-season at Emerald Headingley under his belt having joined mid-year.
“I am enjoying it,” he said.
“We seem to come really good last year towards the back end and we’ve been building onto that for next year.
“We’ve definitely been training hard here at pre-season and we’re looking forward to the new season now.”
He made 14 appearances last term and, on adapting to Super League, the ex-Wests Tigers forward added: “It’s a bit quicker.
“There’s a bit less wrestle so we’ve been putting in a lot of miles out on the pitch in pre-season.
“It has been tough but we’re going to come back a lot fitter and stronger.”
Seumanufagai hopes to play in the Boxing Day friendly against Wakefield Trinity.
He said: “The boys are saying you get a good crowd there and a good atmosphere so I’m definitely looking forward to that.”
In other squad number changes, Cuthbertson will wear No 17 - as he did in 2015, his first season at Rhinos when he finished as runner-up in the Man of Steel and helped Leeds to their historic Treble success.
Scrum-half Richie Myler will wear 16 in 2020 while Crosby - having been frustrated by injuries - will hope to kick-start his Rhinos career in No 18.
New signing from Huddersfield Giants Alex Mellor wears No 11 and several of the club’s academy stars have also been awarded squad numbers for the first time in their careers, with Sam Walters (27), Jarrod O’Connor (33), Jack Broadbent (34) and Corey Hall (36) all promoted to the first team.
Leeds Rhinos squad numbers: 1 Jack Walker, 2 Tom Briscoe, 3 Harry Newman, 4 Konrad Hurrell, 5 Ash Handley, 6 Rob Lui, 7 Luke Gale, 8 Ava Seumanufagai, 9 Kruise Leeming, 10 Matt Prior, 11 Alex Mellor, 12 Rhyse Martin, 13 Stevie Ward, 14 Brad Dwyer, 15 Liam Sutcliffe, 16 Richie Myler, 17 Adam Cuthbertson, 18 Dom Crosby, 19, 20, 21, 22 Cameron Smith, 23 Callum McLelland, 24 Luke Briscoe, 25 James Donaldson, 26 Alex Sutcliffe, 27 Sam Walters, 28 Tom Holroyd, 29 Corey Johnson, 30 Muizz Mustapha, 31 Dan Waite-Pullan, 32 Tyler Dupree, 33 Jarrod O’Connor, 34 Jack Broadbent, 35 Wellington Albert, 36 Corey Hall.