Pyrosomes are pretty cool. 

I upvoted specifically to make the total likes 69 for this post. \o/

Looks like a giant condom

Yes.

I misread it to "sperm whale" and automatically thought of "sperm of whale"
And just "how do I know how big sperm of whale is to compare this thing"

It's actually a colony of much smaller animals, and is apparently bioluminescent.

Those are the limbs of a lovecraftian monster. We can only perceive so much.