HOUSTON -- Already the league's second-youngest team entering the weekend, the Astros are preparing for a new crop of young talent, starting on Monday.

The club called up touted shortstop Jonathan Villar from Triple-A Oklahoma City and designated popular veterans Carlos Pena and Ronny Cedeno for assignment.

No. 4 prospect Jarred Cosart, as was previously announced on Friday, will be recalled and start Tuesday's game vs. the A's.

But Cosart already has a game under his belt (a win against Tampa before the All-Star break), so it's Villar who will be making his much-awaited debut as the starting shortstop Monday against Oakland.

"The challenge for [Villar] at this point is at this level, not in Triple-A," general manager Jeff Luhnow said. "We saw what kind of spark Cosart gave our team in Tampa, so we're hoping both players will provide that up here."

Villar has already been named the everyday shortstop, potentially ending the platoon situation that has prevented consistency at the position this season.

Cedeno's played 41 games at short, Marwin Gonzalez saw action 48 times there before being optioned back to the Minors and Jake Elmore's held down the fort for the last three weeks.

But Cedeno and Gonzalez weren't hitting and Elmore, who isn't a natural shortstop, has committed four errors and misplayed several other balls at the position.

"It's about the fact that Villar's ready and we need to get a long extended look at him," said manager Bo Porter. "There were other shortstops we had an opportunity to evaluate and give playing time to and it's now time to move forward. We believe this guy can be our shortstop of the future."

Villar has hit .278 with the Redhawks this season, hitting eight home runs and swiping 31 bases in 38 attempts. He brings speed and solid defense, or at least that's what Luhnow and the Astros are hoping.

"He's been a shortstop his entire life, so we feel he has the tools to be a shortstop on a championship-caliber team," Luhnow said. "Now's the time to find out. Elmore has the ability to play four or five positions, whereas Villar is a natural shortstop and has great speed on the bases. He adds an element to the game we don't have a lot of up here."

The moves were sudden, but not entirely unexpected with the Astros now 31 games below .500 after Sunday's 12-5 loss to the Mariners and desperately needing some excitement with only five wins in the last month.

"I wouldn't say shocking, but it's something you never put in your mind," Pena said. "I don't dwell on those kind of possibilities. I was an Astro until the end. I still have the hat on."

Pena and Cedeno's departures were met with gloom in the young Houston clubhouse, where the two veterans were gregarious figures and popular with most of the squad. Jose Veras, Jose Cisnero and Carlos Corporan all exchanged lengthy goodbyes and hugs with the duo after Sunday's game.

"I really believe in what's going on in this clubhouse and that Bo's the right man for the job and what they're trying to accomplish," Pena said. "It was truly a pleasure to be part of it. I'm very sad, because I made a lot of friends who are special people. I'm very appreciative of what the organization did for me and that they gave me an opportunity."

Pena was hit-or-miss with that opportunity this season, hitting .209 with eight homers and 25 RBIs in 85 games. But those numbers must be looked at in terms of the salary figure he carries, with a one-year, $2.9 million contract attached to that production.

Unless a team claims Pena off waivers this week, Houston is sill responsible for about $1.2 million of that contract. But there could be some suitors for the 12-year veteran, who has played on contenders before in Tampa, Detroit and Boston.

"I believe in my ability," he said. "It's hard to map what's next out at this point, hard to visualize it. When another opportunity comes here or whatever happens, hopefully it'll be soon and I'll sprint through a new door and embrace it."

Luhnow said the move is in line with the organization's attitude toward another season in the doldrums, with a positive attitude still permeating the front office due to the wealth of talent coming up through the Minors.

"We want to win more games, obviously, but we're not disappointed in the progress we're making as an organization," Luhnow said. "All of our young players are taking steps forwards, some of them big steps forward. What we're focused on is where the Astros are going as an organization."