Merino completed the switch last week and was presented to the local media today.
"Thank you for the interest you have set and for making me feel at home from day one. I'm happy to be with my peers and everyone in the club. I'm in the right place to grow as a person and as a player.
"For me it is something very nice to be here," said Merino.
"I wanted to come back to La Liga, I've been in other leagues, I've seen how things work abroad and I want to show that I can be important in the Spanish league."