Strange tiny creatures helpful or harmful

Hello,

I have been noticing some weird creatures in my tank. Like pinkish worms with white spikes all over, that are see through enough where I can see their digestive system and (poop) in their bodies. They are about 2 inches in length. They are usally under the sand but when the lights come on they are still out for a bit.

I also noticed a clear creature about 1/4 of an inch long that is almost ghost like it floats near the sand. shaped like a -U-, or a plastic grocer bag blowing in the wind.

What could this be we are very curious???????

I found this post on another site . And it sounds like the same thing but they don't seem sure either. I hope this helps find exactly what it is. Stephy24

Strange creature
I recently set up a pod tank as a back-up feeding system for my spotted
mandarin. She eats frozen (Cyclop-eeze, Mysis, etc) and live foods so she is
pretty fat. Anyhow, I purchased some macroalgae for the tank along with
some rubble. I guess this is where the hitchhiker came from. It is
completely clear and hardly noticeable until is it reaches about 1/4-inch,
then it turns milky white. It kind of looks like a jellyfish, but it moves
along the glass like a snail. It is basically a flat round/oval shape with
what I call "tuxedo tails". In its center is a small pink area. They do
not seem to grow over 1/2-inch and are very interesting to watch, but I am
worried about them getting into the main tank since I don't know what they
are. They seem very happy in the tank and are multiplying quickly.
I have tried to attach a crude drawing to give you an idea of the shape.
Any idea what they might be?
Thanks.
Sandy T
<Mmm, maybe a flatworm, perhaps a type of shell-less mollusk (sea slug)... at any length, not likely harmful... At most I'd try siphoning them out while doing other maintenance work... In all likelihood they will "disappear" of their own accord at some point. Bob Fenner>

Im not real sure but maybe they are planteria (sp?) these are like little worms that live on the glass and hide in the sand. These creatures are not harmful but occur because of over feeding maybe try reducing the amount of food you are giving and see if that helps

Aimee