Weird pest in my tank

[un-erasable pencil]

Hi, I posting to ask if anyone knows what these little insect looking things are in my fish tank. There are a lot crawling on my anubias and some on the glass. I also noticed my anubias has been kind of rotting which wasn't an issue before and I've have it for about 4 months. Not sure if that's related to this though. The anubias is also the only plant I have and these things weren't there before. I noticed there are some little round ones and some worm like ones which are all moving around.

 

[GaryE]

Could they be very young pond/pest snails? Is there a shell?

 

[MaloK]

The first one looks like a detritus worm.

Are the round ones able to move rapidly and swim freely ?

 

[AdoraBelle Dearheart]

In one of the photos it looks like a stretched out planaria to me.

If there are planaria, don't panic, but getting an ID would be useful. Are you able to capture one and get some clearer photos of it, macro shots? Or look at it under a magnifying glass, and especially look for the triangle shaped head. Lots of images of them on google if you're unsure.

But when I caught a couple in my tank and removed them, they can stretch out long and thin like that, and the darker middle is similar, and I think I can make out a triangle shaped head in one of those images, but with the blurriness it's hard to tell.

 

[AdoraBelle Dearheart]

Oh, and yes, the round ones look as though they may be baby bladder/pond snails, which aren't a problem really, but some people don't like having them. Have you seen any adult snails around? Both planaria and pest snails like bladder snails can easily sneak into tanks via live plants.

 

[un-erasable pencil]

Update:
I haven't seen another one of the worm-like organisms again so I'm not sure what happened to those.

But, I think you guys were right about the little round creatures. Today, I saw what looked to be a pond snail. Still not sure how those got in there since I haven't added anything to the tank since I got it.

Thanks everyone for all the suggestions!