Are we sure these are colonial hydroids?

[duberii]

I found some of these in my tank- and I'm really not convinced that they're colonial hydroids. Every single ID thread I've come across has them labeled as colonial hydroids, but based on a few observations I've made, I'm not convinced. Here are some pics of the exact type I'm talking about:


The first thing you notice is that they're bright green under the right lighting, which makes me think they're at least partially photosynthetic, which I had never heard of for a hydroid. Also, they have hard tubes, and when I blow on them with a pipette, they retract into the tube much like a feather duster. I saw somebody suggesting it was part of the class Anthozoa, which would make it either a coral or an anemone... I'm not convinced on that either. Perhaps a species name is what I'm looking for, but I haven't seen anything beyond "colonial hydroid" for these. Any help would be greatly appreciated.

 

[shred5]

They certainly look like hydroids but which kind who knows there are lots. I doubt there is anyone who could actually id them on the forums.
People like to lump hydroids together in the hobby and all are bad just like Flatworms.
Truth is most are not just like flatworms and most will die off or do very little.
The whole kill everything panic over everything just makes me laugh. It is so bad on Facebook it has become a joke.

There are some that can become a real problem for sure. If they are popping up all over and forming clumps I certainly would keep an eye on them.

 

[Mikeneedsahobby]

I have those exact invaders. I always assumed they were colonial hydroids. But this is based on what I read here and of course could be wrong.

i treated my tank with fenbendazole. They were irritated but came right back after I added carbon. I tried 3 treatments of fenbendazole spaced two days apart. They looked dead at first but about a week later I see them reopening.

 

[Crashnt24]

These are the same ones I have as well. I always thought they were hydroids for the fact that they sometimes go into the medusa stage and drop eggs into the water column. I have seen it a couple times happen when I'm doing water changes and have stopped all flow. That's how they spread in the reef tank. I now have patches of these everywhere In my tank, it drives me nuts.

 

[duberii]

These are the same ones I have as well. I always thought they were hydroids for the fact that they sometimes go into the medusa stage and drop eggs into the water column. I have seen it a couple times happen when I'm doing water changes and have stopped all flow. That's how they spread in the reef tank. I now have patches of these everywhere In my tank, it drives me nuts.

Interesting- I have never seen them in a medusa phase- that would certainly make them hydroids (or at least jellyfish in a polyp stage). Do the hydroids look like the extended part of the polyp (as in fluorescent with green stringy tentacles), or do they have a different appearance?

 

[Softhammer]

I too have these neon green ones. Been in my tanks for over 20 years and have never ever caused any problems. They do grow on under hangs so I’m pretty sure they are not photosynthetic. I too would be curious to know more about them.

 

[Brew12]

I am not aware of any species of hydroid that creates a hard tube. I believe these are some type of invasive tube worm/feather duster.

 

[Mikeneedsahobby]

I am not aware of any species of hydroid that creates a hard tube. I believe these are some type of invasive tube worm/feather duster.

I’m not the op but the thing I have in my tank looks identical. The tubes aren’t hard. They just look hard. They bend if you push on them.

 

[duberii]

I’m not the op but the thing I have in my tank looks identical. The tubes aren’t hard. They just look hard. They bend if you push on them.

I didn't even think to push on them- good to know

 

[afishbestservedcold]

I have the exact same ones, theyre some sort of small feather duster or tube worms, definitely not hydroids. I love mine, they have the same neon green you described and are nice and thick like youre. keep em!

 

[Softhammer]

There not tube worms, the tubes aren’t calcified or brittle, they’re more leathery. Also love how it’s immediately labeled invasive because the identification isn’t clear. Cancel culture in progress. I can assure you in 20 years of growth they are anything but invasive.

 

[samnaz]

100% these are hydroids. I have the exact same guys in my tank.

 

[samnaz]

I’ve had a clump of about 20 polyps in my tank that hasn’t grown a bit not even in 4.5 years.

 

[czynot]

i have same exact ones in between my clove polyps. they are feather duster worms. very small. color is green under blue light. they dont spread.

 

[thrillreefer]

I have had these for years too, slowly growing on live rock. They're quite pretty, especially under blue lights! I haven't noticed anything bothered by them, some are growing directly among clove polyps, for example, and no issues observed. I do think they're spreading faster since I've started feeding corals more regularly, but I'm not concerned at all.

I love their delicate flowing tentacles


(click on the gif for higher quality at giphy site - resolution is low on R2R)

 

[afishbestservedcold]

https://reefs.com/2016/01/04/iramo-highly-dangerous-aquarium-coral/

See the photo a ways down, I think thats what these are. I haven't tried touching mine yet, has anyone been stung by them?

 

[rhdoug]

Yes I have. I hate them. My advice would be to kill them however you can before they spread, I have them everywhere now. I would not advise touching them with bare skin. The stings last for at least a week to 10 days on me, and itches like crazy.

 

[melfish]

I have no I.D. but just to add to the collective experience- I have had these in my tank for at least 2-3+ years now. Identical to OP’s photos. Came in on a zoa rock. Doesn’t seem to bother anything. Very slow growing- I’m not even sure the original colony has grown at all. Only just recently has spread a very tiny to one other place in the tank, on the other side- must have been through the water column. Mine are not in shaded areas, but on the side or top of rock work. My tank is high nutrient soft & LPS reef, no skimmer.I have no idea if they sting or not because they retract into their tubes before I ever get close enough to risk stinging. Never had to put any thought into avoiding them during maintenance etc.

My personal opinion, so far, is that they are not a threat. They don’t bother anything around them, grow very slowly and don’t spread quickly/often/effectively.

 

[melfish]

I found the following post by @Lionfish Lair helpful and thought others here might also be interested

Those tubes are little protective holsters called the thecal sac. Hydroids without this structure (athecate hydroids) wouldn't have done so well in the dip. I never did anything about mine. The athecate colonies with the unprotected polyps seems to easily spread individually all over the place. The tubed hydroids, tend to grow out from that little colony and never sprouted up here and there all over the place. If you grab one of those stalks and pull, you'll probably find they aren't easy to remove, but they are easy to mow with scissors, if you ever want to go that route

EDIT: Sorry, I can’t figure out how to quote properly- it said the quote was attached properly but when posted it disappeared. So have copied & pasted the text, and it’s from here:

Tubular growth with bright green heads that retract

Are we looking at this...

www.reef2reef.com

 

[Goaway]

If you want to keep your hydriods, keep them. But in some aquariums they take over and kill whoever they want. Corals, and anemones cannot fight back. Thriving hydriods want a territory, they are going to win.
Advice is to get rid of them for a reason. This isn't cancel culture.
Having a variety of animals in our aquarium creates a war zone. It's our job to keep it in check.
If someone wants to observe and see they are of no issues in their system. Thumbs up to that person.