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He is joined in the squad by four uncapped players: New Zealand-born flank Hugh Blake, Glasgow prop Mike Cusack, South Africa-born Edinburgh prop Allan Dell and Edinburgh hooker Stuart McInally.
Head coach Vern Cotter will name his starting XV for the clash at the Aviva Stadium on Thursday.
"It's amazing," said Pyrgos, 26, on being handed the captaincy.
"I didn't expect to be in this situation, but finding out about this is the proudest day of my life.
"I know my family are thrilled too, but I want to now justify it by going out and putting on a good performance."
The squad is missing several key players, such as regular captain Greig Laidlaw and second-row brothers Richie and Jonny Gray.
With Laidlaw and his understudy Sam Hidalgo-Clyne not selected, Pyrgos is determined to seize his chance to prove that he deserves a place in Cotter's final squad for the World Cup.
"The competition in training is pretty fierce and I'm just lucky to be involved," he said. "Now I've got the opportunity to play this weekend, do well and put down the first marker.
"Vern has already spelled out that every jersey, from one to 15, is still up for grabs. He wants to see people improve in training and in games.
"If you do that you are putting yourself in a great position to get a shirt at the World Cup."
After playing Ireland, Scotland will also face Italy twice and France as they gear up for their opening World Cup Pool B match against Japan in Gloucester on September 23.
Cotter will trim his 47-man training squad down to a final list of 31 players for the tournament on September 2.
The 22 players not involved against Ireland on Saturday will continue training at Murrayfield.
Scotland squad named on Tuesday for a 2015 Rugby World Cup warm-up match against Ireland at Dublin's Aviva Stadium on Saturday:
Forwards (14)
John Barclay, Hugh Blake, Fraser Brown, Blair Cowan, Mike Cusack, David Denton, Allan Dell, Grant Gilchrist, Ryan Grant, Jim Hamilton, Rob Harley, Stuart McInally, Gordon Reid, Jon Welsh
Backs (11)
Dougie Fife, Sam Hidalgo-Clyne, Peter Horne, Ruaridh Jackson, Sean Lamont, Henry Pyrgos (capt), Tommy Seymour, Greig Tonks, Richie Vernon, Tim Visser, Duncan Weir
