ID help please

[AlienSpawn]

I have had this new creatue for a while, so far nobody has been able to ID it. It looks a little like a yellow ball sponge, but it has spikes and actually moves. Not very fast but it has moves about a foot over the last few months. It stayed in one spot for a while and appeared to have babies. There are several small bumps that look similar to it where it was hanging out for a while
It is in my gallery, please click on the camera icon above this post. It is labeled, "unknown creature? Please help

 

[lancer99]

Check this out: http://jeb.biologists.org/cgi/content/abstract/209/15/2839

And this: http://www.bio-pro.de/de/region/stern/magazin/01044/index.html

My German is lousy, but one bit I understand is "Tethya can not only move, but can surprisingly strongly contract."

The pic in the second link looks almost exactly like yours.

HTH,
-R

 

[LeslieH]

Tethya or a related sponge - very cool!

 

[boomsticks]

I have one of those on a rock too! I have been trying to figure out what kind of sponge it was for the longest time! Awesome thank you!

 

[boomsticks]

I have one and have been trying to figure out what kind of sponge it was for the longest time. Mystery solved! Thank you!