Flatworms????

Looks like it could be, can't quite tell. If so one of the best ways I have gotten rid of them is to get a Christmas wrasse or something like a coris wrasse they will eat them.

It doesn't look like a flatworm from what I can see. It does look more a some type of pod. Take a look at this website it should help:

http://www.xtalworld.com/Aquarium/hitchfaq.htm

Its hard to tell from that picture, I would say you have a chance that it is, or a chance that its more of a pod (which im leaning towards)

I would get a wrasse just to be safe..... plus what a great excuse to go and buy a new fish!

BTW have you introduced anything new to the tank in the last month or so? (Curious because they all of the sudden started to appear)

I say flatworm too.  Especially from your description of it.  Best fix I have found is Yellow Tail Blue Damsels.  Wiped out an infestation in my tank a few years ago and my original school of 10, now 6, has never been problem children in my tank.

My yellow coris wrasse and melanarus wrasse are kinda my flatworm and other pest insurance. I dont think I have an issue with them, but while I have the wrasse I shouldnt ever get surprised by a sudden boom of pests.

Welcome to the WMAS, one of the best places in the world for factual info about Reefkeeping.
I agree completely with Reef'd Up.
As soon as I saw it knew it was a flatworm just like the ones that grew in my Nemo Nursery. Mostly clear to cloudy white color.
Those are not harmful, I'll post a pic below of the Flatworms that can get out of control and be unsightly, though they are not really harmful either.

The fact is, 99.9% of the species of animals we see in our reef aquariums are not harmful. They are part of the healthy ocean ecosystem that we are trying to replicate.

These "digitate hydroid worms you are speaking of, I'll bet they are not harmful either. Some new hobbyists see what are called Bristleworms and get real worried. Not to worry mate. They are actually part of the cleanup crew of a healthy reef aquarium. I'll post a pic of the way they look when the hobbyist feeds too much and they have just been eating the overfeeding.

For other helpful Reefkeeping Tips found right here on this MB, see the links in my signature line

Nuisance Flatworms


Overfed Bristleworm population and the best trap made with bridal veil netting wrapped/tied loosely around a cube of frozen meaty food with fishing line. Just pull it out when it's tangled with Bristleworms.

Me too that last pic is just creepy!!!

I agree with Reef'd Up.
Again, 99.5 of the species we see in our tanks are never a problem. The remaining 0.5% we know how to handle.
If the tank is left alone and new things are left to live out their lives, you will be constantly amazed at the new organisms you see for a while, but then never see again or glimpse a few months later.
An aquarium evolves and matures as it grows. It is always changing.
Every tank is different depending on the differences in the individual items that went into the tank. What "many" people call a problem may never get out of hand in your tank.
Be careful not to try to control things, but rather let the tank do it's thing and watch the amazing transformation that occurs as it grows and matures.

The information in these two Tips links should be very helpful: