Spitz was signed after Unger was injured in Seattle's Week 3 win over Jacksonville, and was active as Seattle's backup center the past two weeks behind Lemuel Jeanpierre, but did not play.
Walters, who is from Kirkland, was signed to Seattle's practice squad late last season and spent training camp with the Seahawks. His signing gives Seattle five receivers on the 53-man roster after having just four last week when Stephen Williams was released to make room on the roster for Bruce Irvin.
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