Tierna Davidson, Kelley O'Hara and McCall Zerboni have returned to the team following injuries. Davidson broke her ankle in September while playing for Stanford. Zerboni fractured her elbow in a match for the U.S. team against Chile, and O'Hara is coming off ankle surgery.
Ellis included four goalkeepers in the camp: Ashlyn Harris and Alyssa Naeher are joined by Jane Campbell and Adrianna Franch. Campbell, returning after her last call-up in April, has three appearances with the team while Franch is still looking for her first cap.
Also included was defender Emily Fox, coming off her sophomore season at North Carolina. She made her first two appearances with the United States in November.
"We recognize that we have formally entered a World Cup year and I know the players' focus and enthusiasm will reflect the importance of the work we have to do in January," Ellis said in a statement Friday.
The roster by position, with club affiliation.
Goalkeepers: Jane Campbell (Houston Dash), Adrianna Franch (Portland Thorns), Ashlyn Harris (Orlando Pride) and Alyssa Naeher (Chicago Red Stars).
Defenders: Abby Dahlkemper (NC Courage), Tierna Davidson (Stanford), Crystal Dunn (NC Courage), Emily Fox (North Carolina), Kelley O'Hara (Utah Royals), Becky Sauerbrunn (Utah Royals), Casey Short (Chicago Red Stars) and Emily Sonnett (Portland Thorns).
MIDFIELDERS: Morgan Brian (Chicago Red Stars), Danielle Colaprico (Chicago Red Stars), Julie Ertz (Chicago Red Stars), Lindsey Horan (Portland Thorns), Rose Lavelle (Washington Spirit), Samantha Mewis (NC Courage) and McCall Zerboni (NC Courage).
FORWARDS: Tobin Heath (Portland Thorn), Carli Lloyd (Sky Blue), Jessica McDonald (NC Courage), Alex Morgan (Orlando Pride), Christen Press (Utah Royals), Mallory Pugh (Washington Spirit), Megan Rapinoe (Seattle Reign).