weird life in my tank!

so my tank as been set up since january/february of this year. all my rock work (live) was added when i set the tank up. i have only placed in base rock since then. that was about 4 months ago. i have not included any new members of the tank until today and one other fish about 2 months ago.
now this is the odd part (for me anyway) i have noticed little baby star fish in my tank. about 3 or 4 of them. where did they come from?
also this guy in the pic below. i also got one of the small starfish in the picture
they are bluish grey in colour!
anyone have any ideas??? ;D
it looks like it makes a outer shell almost like a tube worm however it looks like a snail inside. it never moves and as it makes the shell it just makes it in circles building over top the old shell.
it sends out this sticky stringy stuff and catches food with it then pulls it back in to eat it. this is very slow. it has antennas too.

 

Asterina star that was a live rock hitchhiker. Almost all are completely reef safe

That's pretty much what it is. A vermited snail makes circular skeletons and fishes for food floating in the water and on rocks.

Here's a macrovideo of one.

Monterey Bay Aquarium: Snail (Vermetid Gastropod) Feeding Video

 

spaghetti worm

 

Spaghetti worms don't have circular shells nor antennae.

 

yep that video you sent, thats him alright. i got another one on the same rock as the Vermetid Gastropod. however its tube isnt circular and its a grey colour.

im glad its not a bad hitchhiker. i have grown fond of him! haha

 

How do you do it? Im sick of my euphylia getting covered in stringy rubbish!

 

thats what she said

 

yea that looks like spaghetti worms...i am not sure about the snail part tho..i have the spaghetti worms and they are red...there are cool but they spit out sandy poop stuff and it gets all over the place:-/