Please help to identify possible worm

[SaltwaterRookie]

I just saw this critter on the glass of my tank this morning, about 30 mins after the lights turned on.

There is no sand in the tank and I dip all my corals before introducing them to the tank. It also looks big enough that I'd think it's been in the tank for a while but I don't know what it is.
It seems to have a sort of "feather" antenna on one side of what I think is its head but I couldn't confirm there are 2 antennas.

I took a video and although it's not very clear I think you can see sometimes the antenna "flowing"? When I came back to check again, about 15 mins after taking video, I couldn't find it any more but it's probably hiding somewhere.

Thank you in advance for any help identifying it!

 

[BristleWormHater]

Likely some kind of nudibranch or flatworm I would take it out and quarantine it as there are many species of harmful flatworms and nudibranchs. If you dont have a qt box, my method is to use a measuring cup and hang it on the side of the tank to maintain water temperature. Try to get pictures of the top of it, is it completely white or is it just the underside? @ISpeakForTheSeas

 

[SaltwaterRookie]

Thank you for the reply! I'm starting to think it's some sort of nudibranch because it really looked more like a slug than a worm. The little antenna or antennas seemed like the feathery antennas nudibranches have but I didn't get a good look at its top to confirm if there's any color or if it's all white. Do some flatworms have antennas?

I'll definitely quarantine it next time I see it again, and I'll be keeping an eye for it. I should have done it as soon as I saw it but it took me so much by surprise and I was in the middle of something else that I didn't react quickly.

Thank you for the tip of hanging a cup on the side of the tank! Good emergency solution.

 

[SaltwaterRookie]

Got it isolated. Better picture and video.

 

[ISpeakForTheSeas]

Thank you for the reply! I'm starting to think it's some sort of nudibranch because it really looked more like a slug than a worm. The little antenna or antennas seemed like the feathery antennas nudibranches have but I didn't get a good look at its top to confirm if there's any color or if it's all white. Do some flatworms have antennas?

Yeah, that's a nudibranch - the feathery antennae are called rhinophores (they're chemosensory organs, so they help the nudibranch "smell" chemicals in the water). Some flatworms do have rhinophores as well, yes.

The little detached mouth part (the crescent shape that's separate from the rest of the body) is an easy way to tell it's a nudibranch in this case.

Based on the body shape, my first guess would be an Arminid nudibranch, probably a Dermatobranchus species, which would feed on octocorals (softies, gorgonians, GSP, etc.) - I can't tell for sure without pics of the top of the nudibranch though.

 

[ISpeakForTheSeas]

Got it isolated. Better picture and video.

Beat me by a second and confirmed my guess - a Dermatobranchus species.

 

[SaltwaterRookie]

Thank you so much for the help identifying! I checked some pictures in internet of the species and you got it @ISpeakForTheSeas, it looks like the Arminid Dermatobranchus.

Having said that, it's a bittersweet finding. I really like nudibranches, even when I know some of them are not coral friendly and this one most likely has been feeding on the soft corals in the tank. I have some gorgonias, leather mushrooms and my favorite one: a fox coral colony, which I now suspect was the vehicle for the nudi to get in the tank. I don't like the idea of getting rid of the nudi (killing it) but I also don't want it to be stressing the corals or munching on them. I also assume without those sources of food it'll starve to death, right?

Do you have any suggestions for a happy compromising solution? I don't have a refugium or second tank I could use for permanent isolation and target feeding. Would a little isolation tank within the display work and I could place a small frag of a softie for it to have its own mini ecosystem or it's not worth it?

 

[ISpeakForTheSeas]

I don't like the idea of getting rid of the nudi (killing it) but I also don't want it to be stressing the corals or munching on them. I also assume without those sources of food it'll starve to death, right?

Yeah, if you have more than one, they can reproduce to the point where they wipeout the corals - if you have just one, it should cause too many issues, but it may still take out a small colony if it strongly prefers one.

It would starve without octocorals to feed on, yes.

Do you have any suggestions for a happy compromising solution? I don't have a refugium or second tank I could use for permanent isolation and target feeding. Would a little isolation tank within the display work and I could place a small frag of a softie for it to have its own mini ecosystem or it's not worth it?

A breeder box/isolation tank with target feeding isn't a bad idea if you've got some fast growing softies that could spare some frags regularly (in fact, this would be great data on the nudibranch's feeding preferences) - you'd want some stuff that grows really fast and/or anything you can confirm it has fed on in your tank, but I wouldn't put anything you'd be worried about getting into the display in the isolation box (so I'd avoid things like blue clove polyps).