The pair are the second and third Wilier riders to head into early retirement in recent weeks, after Marco Coledan announced he was hanging up his wheels at the end of October.
Koshevoy ends his career at the age of 27, having turned pro at WorldTour level with Lampre-Merida in 2015. That season he won a stage at the Tour of Quinghai Lake and finished second on a stage of the Vuelta a España. After riding the Giro d'Italia and Vuelta for Lampre in 2016, he stepped down to Pro Continental level in 2017 with the Wilier team.
Announcing his retirement on social media, with a picture of some of his jerseys, the Belarussian said: "I started down this path in 2006. Thank you for everything, cycling. What a school of life it is. It's now time for a new chapter in my life."
Barely 24 hours later, Turrin announced his own decision to end his career at the age of 26, just two years after turning professional.
After racing at Continental level with the UniEuro team, winning a stage of the Tour du Maroc in 2016, Turrin joined Wilier in 2017 and finished 86th at this year's Giro d'Italia.
"Here we are. The right day to say goodbye. I close a beautiful, happy and proud page of what I have done," he said.
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"Sometimes you need to have the courage to take matters into your own hands and move on. I enjoyed it all and I thank those who have always believed in me, even when I was just a crazy obsessed kid. With my head held high I tell you… it was a nice story."
Koshevoy and Turrin follow former Trek-Segafredo rider Coledan, 30, who announced at the end of October that he was calling it a day after failing to find a contract for 2019.
The Wilier team appears to be cutting down its roster, with fewer than 10 riders officially confirmed for 2019.
