TOS s2e6 “The Doomsday Machine” and VOY s5e14 “Bliss”
The telepathic pitcher plant was approximately two thousand kilometers wide, and contained large amounts of bioplasmic energy.
So, the giant cone is slightly larger in overall length than just the width of the “face” on the giant ship devouring mouth.
BananaVoyager for scale:
Oh jeez, I really must be high! I don’t know what I was thinking; space whales would eat space plankton, not space jellyfish. It’s chelys galactica that would eat Farpoint cnidarians.
Now, which of these things is most plankton-like?
Now, hang on a minute. Picard introduced its own brand of space faring “chum”:
But, for arguments’ sake and our own personal gratification, let’s assume the space whales require certain nutrients that are only locally available from crystalline entities.