is this bristleworm good or bad?

[spemin]

Sorry the pix came out blurry; my digical focused on the background instead

 

Anyway, I'm pretty sure it's a bristleworm, and a violent one at that (maybe cuz it was panicking) because it would violently curl up and seemingly constrict repeatedly

 

Anyway, I've removed it from my tank into a cup until I can determine whether it's good or bad.

 

Also, what are those black round things in the upper left? Thanks in advance!

[spemin]

there's also a smaller, flatter, black and white striped worm. i wouldn't mind keeping it if it's harmless and helpful : )

 

lastly, there's this thing that looked like a small mussel, but when i poked it, it was actually something else and it retracted into the hole it was in! I'll try to get a pix when it comes back out, unless someone already has an idea of what it is. i don't think it's a worm, although i have so many ; p