Ctenophore.

Public Domain from NOAA photo library - this page has now vanished but has been saved at Internet Archive, dated 12 Dec 2006.

Image ID: nur01002, National Undersearch Research Program (NURP) Collection
Credit: OAR/National Undersea Research Program (NURP)

The cited web page does not specifically say this is a beroid. However the very similar The Jelly Connection identifies a Beroe specimen attacking another ctenophore.

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