* FTSEurofirst 300 sags 0.6 pct, down 9 pct so far this week
* Central banks' cash injections fail to stop the selloff
* HBOS jumps 17 pct after takeover by Lloyds
By Blaise Robinson
PARIS, Sept 18 (Reuters) - European stocks ended lower on Thursday after a rollercoaster session, as a coordinated move by the world's leading central banks to ease the credit squeeze failed to halt the equities selloff that started on Monday.
The FTSEurofirst 300 <
> index of top European shares closed 0.6 percent lower at 1,063.62 points, falling for the fourth straight session and ending at its lowest closing level since April 2005.The index has lost around 9 percent so far this week, and is on track for its biggest weekly drop since the attacks of Sept 11, 2001. The declines follow Lehman Brothers' <LEH.P> collapse, the takeover of Merrill Lynch <MER.N> and the bailout of insurer AIG <AIG.N>.
"There are a lot of pending issues in the financial sector, and probably a lot of bad surprises in the pipeline," said Jean-Claude Petit, head of equities at Barclays Wealth Managers France.
"This crisis constitutes a turning point in the business model of banks and the way Wall Street works. Consolidation among banks is inevitable. But these are "arranged marriages" under the pressure of the U.S. authorities."
The world's top central banks joined forces on Thursday to throw a multi-billion dollar lifeline to global markets in a dramatic effort to free up bank-to-bank lending, frozen by the turmoil on Wall Street.
In an unprecedented move, the U.S. Federal Reserve made an extra $180 billion available to major central banks to lend on to their local commercial banks in a bid to get dollars circulating in overnight and term money markets.
European banking stocks, which had had a tentative recovery earlier in the session, ended the day mixed.
UK lender HBOS Plc <HBOS.L> jumped 17 percent after Lloyds TSB <LLOY.L> said it would take over the embattled UK lender in a $22 billion deal helped through by the government. Lloyds sank 15 percent.
Barclays <BARC.L> was down 5.3 percent, Royal Bank of Scotland <RBS.L> down 4.5 percent, while BNP Paribas <BNPP.PA> rose 3 percent and Credit Suisse <CSGN.VX> gained 2.8 percent.
"Recent events should not come as a surprise to those who, like us, see the U.S. economy sliding into deep recession as a result of long years of grotesque debt excess," Albert Edwards, strategist at Societe Generale, wrote in a note.
"Amid recent chaos, few realise that the next phase of de-leveraging has only just started."
U.S. stocks were also in the red on Thursday, hit by concerns over the fate of investment bank Morgan Stanley <MS.N>, whose stock tumbled 22 percent.
Adding to the gloom, U.S. asset manager Putnam Investments said on Thursday that it had closed its $15 billion Prime Money Market Fund due to redemption pressures.
Stock exchange operators Deutsche Boerse <DB1Gn.DE> and the London Stock Exchange <LSE.L> gained 7.5-7.9 percent, with traders citing increased volume and speculation that investors could move away from alternative trading platforms such as Turquoise back to more established ones.
German carmaker Volkswagen <VOWG.DE> soared 27 percent. Traders mentioned short-covering sparked by expectations that Porsche <PSHG_p.DE> would raise its VW stake further. Volkswagen shares have rallied strongly over the past few sessions, after Porsche announced it had raised its stake in VW to over 35 percent.
"It has hardly anything to do with fundamentals, it is just a short squeeze, people covering short positions -- and maybe Porsche or third-party buying," said Robert Heberger, an analyst at Merck Finck.
Across Europe, the FTSE 100 <
> index fell 0.7 percent, Germany's DAX < > eked out a gain of 0.04 percent and France's CAC 40 < > lost 1.1 percent.So far this year, the FTSE 100 is down 24 percent, the DAX is down 27 percent and the CAC 40 is down 30 percent.
(Reporting by Blaise Robinson; Editing by Erica Billingham)