Hitchhiking on blue hypnea

[bmistler1]

Can anyone identify this organism that is growing on my blue hypnea? The tentacles extend and retract throughout the day.

 

[SaltySqueeble]

Probably aiptasia.

 

[ZzyzxRiver]

My blue hypnea came with a Medusa worm (a kind of sea cucumber), and their head sort of looks like that. Look those up and see if yours acts like the description, maybe.