What is this?

[Joe Pusdesris]

It is not a sponge, it is definitely alive and doesn't like light.

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It looks like a huge flat snail, but I don't think all of that is coming out of that little cerith...

 

[SushiGirl]

From what I can tell in the pics it looks like a polyclad flatworm.

 

[Joe Pusdesris]

Are they problematic?

 

[SushiGirl]

I've never had them, so I don't know what they're capable of.
I'm sure if you do a search here on them, you'll find all kinds of stuff tho!

 

[Joe Pusdesris]

Thanks! It is really quite big.. Most of it is inside that rock, which is worrying. I haven't added anything to the tank in oh, probably a year so it has been in there for a while. I suppose it doesn't eat coral or fish...

 

[SushiGirl]

I don't think they eat fish, but I think the majority of flatworms eat coral. Just not sure...since I never had them, I never read up on them LOL.

 

[Joe Pusdesris]

It may actually be eating that cerith snail... Apparently they are known for eating snails from what my googling turned up.

 

[SushiGirl]

Uh oh!

 

[Sebastian J.]

It's a Purse Shell or Reticulated Flatworm, Pericelis sp. They're mollusc predators. They prey on all kinds of snails and clams, unfortunately including Tridacnas.

 

[mscarpena]

It's a Purse Shell or Reticulated Flatworm, Pericelis sp. They're mollusc predators. They prey on all kinds of snails and clams, unfortunately including Tridacnas.

Hes right get rid of it.

 

[Joe Pusdesris]

It's not easy to get rid of...