Weird “Aliens” in my shrimp tank!

Today when I feed my shrimp pets, I realize to my horror there are some weird “aliens” crawling around the gravel of my shrimp tank!! Ahh!!

I immediately took out my video camcorder to film it down to find out more about this weird creatures! It’s very small and creepy snake like creature that slide around the gravels.

Anyone with information abut this weird “aliens” do let me know please! :3
[youtube]http://www.youtube.com/watch?v=UnosCGntYAE[/youtube]

UPDATE: Just found out they are Planaria, flatworms!! AHHH now constructing a trap to catch them all!! MUAHAHAH