MLS champion Toronto, D.C. United, New England Revolution and Real Salt Lake have the most selections with three each.
Four players played for the USA in the 2017 Under-20 World: Danny Acosta, Justen Glad and Brooks Lennon from Real Salt Lake and Tyler Adams from the New York Red Bulls.
Only five MLS clubs aren't represented: Atlanta United, Houston, Montreal, Portland and FC Dallas, which didn't release its players because of its preparations for the Concacaf Champions League.
Eight players played for the USA when it won the 2017 Gold Cup: Juan Agudelo, Dom Dwyer, Bill Hamid, Kelyn Rowe, Justin Morrow, Cristian Roldan, Gyasi Zardes, Jordan Morris, who scored the winning goal in the final, and Arriola.
Fifteen players are looking for their first cap: Alex Bono, Cody Cropper, Zack Steffen, Tim Parker, Matt Polster, Russell Canouse, Marky Delgado, Marlon Hairston, Ian Harkes, Nick Lima, Ike Opara, Christian Ramirez, Acosta, Glad and Lennon.
Adams is the youngest player in camp at the age of 18.
Morrow is the oldest player in camp at the age of 30.
Zardes has the most caps with 37.