Financial stocks spiraled downward Monday as Citigroup's ( C) furiously traded losses trampled the sector. Citi's much-maligned CEO, Chuck Prince, finally resigned over the weekend, but the banking giant also estimated current-quarter writedowns of between $8 billion and $11 billion from the shrinking value of its subprime-related investments. And, as disclosed in its quarterly filing, Citi also shaved 3 cents a share, or $166 million, off its previously reported third-quarter profit tumble to a restated 44 cents a share. Fitch lowered Citi's debt rating and Standard & Poor's put it on negative credit watch, though Prince's departure prompted Punk Ziegel to upgrade the stock to market perform from sell. Citi Europe Chairman Win Bischoff will serve as acting CEO while a permanent replacement is sought, and Executive Committee Chairman Robert Rubin will assume Prince's former Chairman position. Citi shares fell 5.5% to $35.67 in very heavy trading. Prince is but the latest executive casualty resulting from the ongoing credit-crunch travesties, joining Merrill Lynch's ( MER) just-ousted CEO Stanley O'Neal and Bear Stearns ( BSC) COO Warren Spector, who was given the boot earlier this year. Shares of the firms gave up 3.8% and 3.1%, respectively, after Lehman Brothers cut both to equal-weight from overweight amid a larger sector downgrade of brokers and asset managers. Citi, Merrill and Bear are among the most egregious examples of big financial-services firms getting crushed by credit woes , but even perceived stalwarts like Goldman Sachs ( GS) and JPMorgan Chase ( JPM) were losing ground Monday. The brokers each recently reported growing and better-than-expected third-quarter earnings, although Goldman stock has since Friday been battered by rumors of big upcoming writedowns .