Could be planaria. I see them in my tanks sometimes, but I don't worry too much about them. It does seem odd to have them with no fish in there though.
Their not like planaria their smaller.
are they swimming or are they on the bottom?
If there is no fish and not much water movement supplemental aeration, are you sure they are not mosquito larva? If they are, hurry up and get some fish in to eat them before they become mosquitoes and start biting.
They are swimming on the top... And I hope I can get some fish soon! I'm not sure if they are mosquito larva...
Well mosquito larva certainly look like wriggly things int he water.
I think they are brown and small.