Anyone wanna take a stab at this one?

[Victor Noda]

Found this one on my refugium today. I wish it was a jellyfish, but it pulses and I dont know what it is.

 

[fish farmer]

Hydroid I believe in the medusa stage.

 

[vetteguy53081]

These are are crawling hydroid jellyfishes, which do not swim, but rather move around the tank sort of like a small, soft, slow spider. They move by fastening on to the substrate with their adhesive patches. The tentacles are tipped with concentrations of nematocysts.
They are not of harm and Keyhole Limpets eat them

 

[Victor Noda]

Thank you so much! I'm glad to hear its not a pest!