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We are carrying out a sensitive blind survey for neutral hydrogen (HI) in theVirgo cluster and report here on the first 5\deg\ x 1\deg\ area covered, whichincludes two optically-dark gas features: the five-cloud ALFALFA Virgo 7complex (Kent et al. 2007, 2009) and the stripped tail of NGC 4522 (Kenney etal. 2004). We discover a sixth cloud and low velocity gas that extends thevelocity range of the complex to over 450 km/s, find that around half of thetotal HI flux comes from extended emission rather than compact clouds, and seearound 150 percent more gas, raising the total HI mass from 5.1 x 10$^8$M$_\odot$ to 1.3 x 10$^9$ M$_\odot$. This makes the identification of NGC 4445and NGC 4424 by Kent et al. (2009) as possible progenitors of the complex lesslikely, as it would require an unusually high fraction of the gas removed tohave been preserved in the complex. We also identify a new component to the gastail of NGC 4522 extending to ~200 km/s below the velocity range of the gas inthe galaxy, pointing towards the eastern end of the complex. We consider thepossibility that NGC 4522 may be the parent galaxy of the complex, but thelarge velocity separation (~1800 km/s) leads us to rule this out. We concludethat, in the absence of any better candidate, NGC 4445 remains the most likelyparent galaxy, although this requires it to have been particularly gas-richprior to the event that removed its gas into the complex.

The Widefield Arecibo Virgo Extragalactic Survey I: New structures in the ALFALFA Virgo 7 cloud complex and an extended tail on NGC 4522