Some kind of flatworms or nudibranch?

[ChrisIC]

Hi guys. I have just spotted these little things in my tank. Does anyone know what they are and if they will cause problems? I dip everything that goes into my tank so I'm really not sure where they came from. To my colour deficient eyesight the look green but I could be wrong. I'm really hoping they aren't a big problem. They seem to have come out of nowhere, I look at the tank every day and I didn't see any before today, but there are a good few in there. I'm going to start siphoning out as many as I can now.

 

[CrimsonTide]

Going to follow as those look super cool but also mildly troubling.

 

[homer1475]

Definitely look to be flatworms to me, but I have no idea what kind they are.

 

[ChrisIC]

Going to follow as those look super cool but also mildly troubling.

Yes, I'm not panicking but definitely quite concerned, this was totally unexpected.

 

[ChrisIC]

Definitely look to be flatworms to me, but I have no idea what kind they are.

I got a close photo of the ones I just removed, they do look like flatworms to me too but I'm clueless after that.

 

[twentyleagues]

@ISpeakForTheSeas ?

 

[IKD]

Looks like a nudibranch

See if this one matches. Do you have a lot of spirorbid worms?

Vayssierea felis - Wikipedia

en.m.wikipedia.org

 

[ChrisIC]

Looks like a nudibranch

See if this one matches. Do you have a lot of spirorbid worms?

Vayssierea felis - Wikipedia

en.m.wikipedia.org

I have a good few spiorbid worms in the tank alright. It does look like Vayssierea felis, but I wouldn't be able to tell for sure. I'm a bit surprised that my wrasses weren't interested in them.

 

[ISpeakForTheSeas]

Looks like a nudibranch

See if this one matches. Do you have a lot of spirorbid worms?

Vayssierea felis - Wikipedia

en.m.wikipedia.org

Yeah, the second pic looks pretty deceivingly like a true nudibranch, but when you take a closer look at the first pic you see they have a leafy shape rather than a solid tube shape. That gives away that these are actually an Elysia sp. Sacoglossan Slug - algae eaters (and they seem to be well fed in the pics):

Elysia flava or E. obtusa - harmless/beneficial Sacoglossan slugs. They're herbivores, with E. obtusa known to feed on Bryopsis, while E. Flava is thought to feed on Cladophora. As mentioned below, I don't know if these are required feeds or just strongly preferred feeds:

Some lettuce slugs (typically from the genus Elysia) will eat nuisance algae species, but their wild diet varies pretty drastically from one species to another, and some species have some pretty specific wild diets (I don’t know if these are required diets or preferred diets, but Reef Cleaners reports that they'll eat just about any green, fleshy algae). That said, Elysia slugs generally feed on siphonalean algae such as Caulerpa, Codium, Acetabularia, Halimeda, Udotea, Byropsis, and Valonia spp. So, in theory, these guys should eat nuisance algae that pops up in your tank.

No - your orange ones show a "leafy" texture on the back (i.e. instead of just being tube-shaped, yours have leafy "wings" on the side that they've folded into the middle; you can see this easily if you zoom in on the orange one on the right in the pic). Your slugs are an Elysia sp. sacoglossan slug like E. flava or E. obtusa.

Edit: To clarify, V. felis and relatives are just tube-shaped; no leafy "wings."

 

[ChrisIC]

Yeah, the second pic looks pretty deceivingly like a true nudibranch, but when you take a closer look at the first pic you see they have a leafy shape rather than a solid tube shape. That gives away that these are actually an Elysia sp. Sacoglossan Slug - algae eaters (and they seem to be well fed in the pics):

That is a big relief, thanks! I'm wondering now if I should put them back in? I suppose I could give them some of the algae I give the fish and see if the start eating it before I put them back in. Or would they most likely have a specific type of algae that they will only eat?

 

[ISpeakForTheSeas]

Or would they most likely have a specific type of algae that they will only eat?

They might take a random algae, but they do have preferences that may be necessary- Bryopsis and Cladophora would be the first to try.

 

[ChrisIC]

They might take a random algae, but they do have preferences that may be necessary- Bryopsis and Cladophora would be the first to try.

I don't think I have Bryopsis or Cladophora in the tank, unless it's somewhere at the back of the rocks where I can't see it. And I'm really surprised that they weren't eaten by the wrasses in the tank, Macropharygodon, Solorensis, Melanarus and Coris.

 

[ISpeakForTheSeas]

I don't think I have Bryopsis or Cladophora in the tank, unless it's somewhere at the back of the rocks where I can't see it. And I'm really surprised that they weren't eaten by the wrasses in the tank, Macropharygodon, Solorensis, Melanarus and Coris.

If you don't have any of those, then you can try other siphonalean algae such as Caulerpa, Codium, Acetabularia, Halimeda, Udotea, and Valonia spp.