mysterious white/transparent upside down umbrellas with hair

[cashemin44]

Looking for some help. A friend and i were examining my tank and noticed these bizarre creatures. I was wondering if anyone knew what they might be and if so are they bad for my tank? I have a 55 gal with rock but its not live. I have a picasso trigger, one clown and regal tang. My levels are normal although my temp for my tank is on the higher side or normal. Any info would be great!

 

[rainbow grouper]

Could you get a clearer picture and thought i might mention suggested minimum tank size for Picasso trigger 75 gallons you do realize they get to about 9 inches don't you.

 

[spanko]

Hydroids.