Got a pretty decent picture of one of the worms in the back of the tank that was fully extended early this morning.
This might be a ribbon worm. It doesn't look like it has bristles or segments. It is smooth, right? I suggest you look them up to be sure. Nemertea ( Ribbon Worms ). You can scroll through all these pages of images if you'd like:
http://eol.org/pages/2855/media (this is the encyclopedia of life (eol) website). There are about 900 known species in the phylum Nemertini (also spelled Nemertina or Nemertea by different authors). So, if you can't find the exact one, don't be to disappointed. Instead focus on the body anatomy of the worm.
If it is a ribbon worm, I'd suggest you capture it and get it out of the tank, the nemertines are carnivorous. Most feed on small invertebrates like crustaceans and annelids.
The below is from this website: Berkeley University (
http://www.ucmp.berkeley.edu/nemertini/nemertini.html)
The most distinctive feature of nemertines is a large
proboscis, which you can clearly see in the image to the right. In one group of nemertines is tipped with a piercing barb known as a
stylet. In other nemertines, the proboscis is unarmed, but often secretes sticky fluid. Normally, this proboscis is retained in a specialized sac in the animal's body, the
rhynchocoel. To capture prey, the proboscis is rapidly everted (turned inside-out) and shot out of the rhynchocoel. It wraps around the prey, and toxic secretions immobilize the prey; nemertines with stylets use them to stab the prey repeatedly, introducing toxins into the body. Generally, nemertines are carnivorous; most feed on small invertebrates like crustaceans and annelids, but some feed on the eggs of other invertebrates, and a few live inside the mantle cavity of molluscs and feed on microbes filtered out by the host.