long skinny creature in my marine setup with little legs

Yep, when I first read the post, I immediately thought of an epitoke. You are correct, they are usually seen after lights out but occasionally you can see them during the day. The do come in different sizes....it all depends on the size of the polychaete to begin with.

For those who don't know what an epitoke is, it's when a polychaete worm reproduces. The back 1/3 of the worm changes into a slightly different form. Eventually, usually after lights out, the epitoke portion of the worm breaks off, swings around crazy like it's on Meth or Crack, and eventually dissolves or explodes sending gametes into the water column to become more polychaete worms.

 

What about an amphipod?

 

Picture!!

 

Good id sounds most logical k+

 

thanks everyone i think its hiding or has been food for some fish, lol