Brett Wilkinson, Jason Harris-Wright and captain Nathan White make up the front row trio. Michael Kearney replaces Ireland international Mike McCarthy in the second row, starting alongside Connacht's most-capped player Michael Swift (234 caps).
December's Player of the Month, Eoin McKeon, returned from injury last week and starts at number 8, joining flankers Andrew Browne and Johnny O'Connor in the back row.
In the province's back-line, Tiernan O'Halloran is named at full-back, replacing Robbie Henshaw who is on international duty this week. Danie Poolman, this season's joint top try scorer (3 tries), and Fetu'u Vainikolo are named on the wings.
Kyle Tonetti will make his first start for Connacht this season following a lengthy battle with a hamstring injury.
The 25-year-old has recovered fully and has been playing with his club, Ulster Bank League outfit Lansdowne, over the last number of weeks.
Tonetti joined Connacht last season from Sale Sharks and was ever-present in the squad. He showed his versatility and ability to adapt, featuring at inside and outside centre as well as a few games on the wing
Tomorrow night in Wales, he will start at Inside centre in a midfield partnership with Eoin Griffin, who was a try scorer against the Scarlets last September.
The half-back pairing of Dan Parks and Kieran Marmion remains in place. Scrum half Marmion will make his 20th senior appearance for Connacht - he is the only player to have started every one of Connacht's games this season.
On the bench there are some welcome returnees with Willie Faloon and John Muldoon named amongst the forward replacements. Regular skipper Gavin Duffy also returns to the fray and could feature against Simon Easterby's side.
CONNACHT (v Scarlets): Tiernan O'Halloran; Danie Poolman, Eoin Griffin, Kyle Tonetti, Fetu'u Vainikolo; Dan Parks, Kieran Marmion; Brett Wilkinson, Jason Harris-Wright, Nathan White (capt), Michael Swift, Michael Kearney, Andrew Browne, Johnny O'Connor, Eoin McKeon.
Replacements: Ethienne Reynecke, Rodney Ah You, Ronan Loughney, Willie Faloon, John Muldoon, Paul O'Donohoe, Miah Nikora, Gavin Duffy.