Not planaria. You’d be able to tell if they were, they have a very distinct spade shaped head. These guys just kind of show up in aquariums and pose no threat. They’re either detritus worms or rhabdocoela flatworms. They might eat something already dead but they’re not going to eat anything living.
Edit: If it doesn’t have eye spots or a spade shaped head that you can easily see with plain eyesight or with a magnifying glass then it’s not planaria.
Now if you still want to get the population in check just do a lot of gravel vacuuming and don’t overfeed. But I’m 99.9% certain those aren’t planaria so I wouldn’t bust out any dewormer.
People often confuse these for rhabdocolea but it looks like a oligochaeta pristina sp to me — is its movement like an inchworm (a bit like a caterpillar)? If so, its oligochaeta. Beneficial to an aquarium though so nothing to worry about.
ayam5 
This looks like rhabdocolea to me. I have em too and so far everything is multiplying readily in my aquarium.
Not planaria. You’d be able to tell if they were, they have a very distinct spade shaped head. These guys just kind of show up in aquariums and pose no threat. They’re either detritus worms or rhabdocoela flatworms. They might eat something already dead but they’re not going to eat anything living.
Edit: If it doesn’t have eye spots or a spade shaped head that you can easily see with plain eyesight or with a magnifying glass then it’s not planaria.
Now if you still want to get the population in check just do a lot of gravel vacuuming and don’t overfeed. But I’m 99.9% certain those aren’t planaria so I wouldn’t bust out any dewormer.
They are not dangerous and are actually a good sign from what I understand
I have had these in my planted ramshorn tank for years. Theyre great little critters, never caused any harm and they must help keep my substrate clean
People often confuse these for rhabdocolea but it looks like a oligochaeta pristina sp to me — is its movement like an inchworm (a bit like a caterpillar)? If so, its oligochaeta. Beneficial to an aquarium though so nothing to worry about.
Planaria are dangerous to shrimp however I’m not sure if these are planaria. Do you see eye spots and an arrow shaped head? How do they move?
I’ve got these in my tank as well. And I have NO fish. Started seeing them a day after I added l bacteria. Should I be worried?