Some kind of flat worm?

[Kilman805]

My son just discovered this on the glass tonight. It looks like some sort of flat worm maybe? It is at least a couple inches long and it crawled fast up the glass, then glided on its back along the water surface until it reached the back wall. It’s top side is speckled like sand. Sorry for the bad photos, lights out at night. It has something that looks like a head with little nubs.

 

[KQuillan]

Looks like a flatworm to me. They are awful and will kill euphyllia.
Dip corals and check for eggs.

 

[Crabs McJones]

Looks like some sort of nudibranch possibly @ISpeakForTheSeas

 

[VintageReefer]

All the flat worms I’ve ever encountered are around .25”

That looks like a sea slug or Nudibranch

 

[Kilman805]

All the flat worms I’ve ever encountered are around .25”

That looks like a sea slug or Nudibranch

It’s much flatter than any photos I see of those.

I caught it last night and threw it in a quarantine tank. I’ll see if I can get a better photo today.

 

[Kilman805]

Here is another photo of him in quarantine. He’s there on the base of the sponge filter.

Note the green mantis shrimp too. Quarantine tank is currently purgatory for questionable hitchhikers.

 

[Cheezle]

looks like a polyclad flatworm to me

Here is another photo of him in quarantine. He’s there on the base of the sponge filter.

Note the green mantis shrimp too. Quarantine tank is currently purgatory for questionable hitchhikers.

 

[Kilman805]

I have no coral in the tank yet. Would it be unusual for this to be a hitchhiker on TBS live rock? If I have one this size, are there surely others? It's very strange that it just showed up after having the tank running over 6 months.

Any suggestions? Keep an eye out for more? Treat with something? Trap?

 

[Kilman805]

Good old thread here:
https://www.reef2reef.com/threads/help-removing-leopard-polyclad-flatworm.932727/post-10542277
This is definitely the same thing as in my tank.

 

[ISpeakForTheSeas]

Looks like some sort of nudibranch possibly @ISpeakForTheSeas

I have no coral in the tank yet. Would it be unusual for this to be a hitchhiker on TBS live rock? If I have one this size, are there surely others? It's very strange that it just showed up after having the tank running over 6 months.

Any suggestions? Keep an eye out for more? Treat with something? Trap?

First pic was tough to work with, but the second pic is clear enough - I agree with flatworm, and looks like one I'd expect to be predatory to snails and/or bivalves. They're not common on TBS rock, but they're not too uncommon in the hobby.

I wouldn't expect more, but I would keep an eye out for more and/or for eggs (these can be quite good at hiding, so I would guess disappearing snails would be the first sign if you've got more).

 

[Privateye]

Definitely a flatworm. I've seen plenty that size in the wild while collecting coral and anemones. You'll commonly find them stuck to the undersides of rocks.