Tube anemone, worm, aiptasia?

[Kobooi]

I vacuumed this out of my sandbed. I thought aiptasia while it was going through the hose (I have some small aiptasia in the tank once in a while, but usually on the rocks, not the sand) but when I saw it in the bucket it looked different, more and thinner tentacles than aiptasia. I googled tube anemone and all kinds of worms, but I only get pictures of thriving live ones.
I kept it in a jar but less than 24 hours later it was dead (when I took the pictures).
Can someone ID it? Thanks.

 

[minus9]

Spaghetti worm. These are a great addition to a tank. Filter feeders and consumer of detritus.