Identification Questions

[fishboytoo]

Hi,

Does anyone know what these are?
First one looks like some sort of bi-valve. I could swear that the thing moves around. One day its where I took the picture then its no where to be seen for two days, then its back. Thought that was strange. I suppose my view could have been obscured by the zoo but that doesn't seem likely. I pulled on it with tweezers and it seems very firmly attached

Then there are these jelly-fish looking things starting appearing on the glass. First just one, now have many of them. I thought some kind of pod maybe. They are very small, about 2 mm diameter.

 

[-Nemo-]

Not sure about the first one.

Second is a hydromedusae otherwise known as hydroids. Basically teeny tiny jellyfish. They have several different forms in their life cycle, the one on your glass is one of them. They are basically harmless and usually come and go (so you'll see them for a while then maybe not see them for months and then they'll come back).
Only bad if you have little baby clownfish they like to sting and kill then eat

 

[fishboytoo]

Thanks Nemo, I thought they looked like jelly fish. I didn't know that there were jelly fish that small.

Anyone have any ideas about that mollusc-looking thing??
I don't know if it was moving or not but yesterday it was hardly visible with the zoos opened up around it. They practically covered it completely, yet the other day it stood out very well, even with the polyps open. Also, there look to be many similar empty shells on my rock.

 

[injektion]

i think it's exactly that, some type of mollusc. i have a few of those in my tank as well. they look like tiny scallops. i wouldn't worry about it being there, and don't try to pull it off or you might run the risk of killing it. they're your basic hitchhikers and are pretty much self sustaining in a reef tank.

cool jellyfish thing though!