Aptaisia or hydroid or...?

[Fishbird]

My tank has been running for 4 weeks today. I just noticed that I have three small aptaisia or hydroids or something else growing on a shaded part of one of my rocks. I’m sure I have more, but these are the three I can see right now. They are white/clear and look like elongated balloons with short tentacles. I will try and get some better pictures but does anybody know what these are?

 

[Mr_Knightley]

those are actually a type of sponge, a sure sign that your tank is thriving! they do absolutely no harm, just don't smoosh them, or you'll get a handfull of spines!
Good luck with your tank! keep us posted.
God bless you!

 

[reef lover]

Yup. Pineapple sponge.

 

[Fishbird]

Thanks! This made my night. I’ve always thought sponges were really cool!