Is this a hydroid?

[jgreen1025]

Dr. Ron,

Is this a hydroid? I've got two little patches of these things on one of my rocks. The longest are maybe a centimeter at most, and the shortest are maybe about 4 mm long. They're brownish and don't seem to harm anything.

http://reefcentral.com/gallery/data/500/58717poss-hydroids.jpg

The links I've tried for your article on hydroids doesn't work, and I haven't found a thread on hydroids showing a similar creature. Any idea what these are?

John

[rshimek]

Hi John,

I am not convinced they are hydroids; they may be, but if so they are oddballs. Can you get a shot of one "down the bore" so to speak showing the mouth, etc. Barring that could you pluck one out and send it to me.

Sorry about the hydroid article, the link is an archive site and sometimes they seem to have problems.

[rach78978]

does the feathery part retract into the longer tube section if you make a sudden movement / shadow?

[jgreen1025]

http://reefcentral.com/gallery/data/500/58717DSC00751.jpg
http://reefcentral.com/gallery/data/500/58717DSC00739.jpg
These are the best photos I can get of them, although neither really shows the "mouth" area particularly well. I had never noticed them retract before - they don't do it merely by movement or shadows - but when I tried to blow them off with a turkey baster they retracted pretty fast. In the top photo you can see the upper tube is retracted and the tube is rather transparent. The second photo you can see the transparency of the tube from the shadow. The little tentacles or strings coming off the top are very flexible and sway all over the place, unlike all the various feather duster worms in my tank, which appear almost rigid. Also, the feather dusters have kind of a "V" shape (when looking at the end) to each of the parts that make up the "collector." These are just little threads. But maybe it's just another kind of feather duster worm after all?

John

[rshimek]

Hi John,

It is possible that they are some type of worm, but your first posted images tend to refute that idea. Worm tentacles are almost always branched, and these tenacles do not appear to be branched. Some hydroids can retract as you have described, but so can some other animals.

Another request... Can try again with getting a crisp clear image of the animal fully extended and from a couple of different angles?

Thanks!

[jgreen1025]

Okay, after about 200 tries (and some re-reading of the camera manual) this is about the best I can get:

http://reefcentral.com/gallery/data/500/58717DSC01008.jpg

Hopefully this is clear enough?!? I vaguely recall seeing something looking very similar in drawings showing the life cycle of things like (I think) sea urchins or something like that. But I have no urchins in my tank. The only thing I've see that spawns into the water column (other that the various worms) are some of my snails, like Trochus and Cowries. Incidentally, I initially saw two groups of these, but I've since found three more - always in little clumps. Anyway, I hope this is clear enough to give some better idea of what they might be. Thanks again for all your help!

John

[jgreen1025]

Just a couple more shots that hopefully show these little creatures well enough for ID. This first one shows a different little clump (surrounded by what I assume are sponges?) and kinda shows the "mouth" area:

http://reefcentral.com/gallery/data/500/58717DSC01015.jpg

And this one shows yet another little clump with some of the regular little feather dusters that are trying to completely take over my tank:

http://reefcentral.com/gallery/data/500/58717DSC01025.jpg

If I'm able to take any more pictures that can show them from a more helpful angle or in better detail I'll upload them. Thanks again!

John

[rshimek]

Hi,

[thanks] for taking the effort to get the new images. It was worth it. They are not hydroids. The structure of the mouth region is pretty definitive. The four part or tetramerous symmetry of the mouth region visible in the first image is quite distinctive.

I believe your critters are the polyp form of a coronate scyphozoan jellyfish. They are possibly in the genus Stephanoscyphus or Nausithoe (there is some confusion in the literature about the proper name). These animals will bud off small "thimble" jellyfish. The polyps are reported to able to inflict a very nasty sting with their nematocysts, so be careful in handling them.

[jgreen1025]

COOL... maybe!?! I've done a search on RC here and found that there's not exactly a lot of info or pictures on them, but they ought to be relatively harmless in my tank (as long as I keep clear of them anyway!). I'll keep an eye on the polyps and try to get some photos of them budding off and of the adults. One question though, a jellyfish book my kids got at the Long Beach Aquarium says that polyps for Moon jellies can bud off up to a dozen or so adults each year and that they'll last for years - does that apply to this kind as well? I estimate I've got around 50-60 of these little brown things now, so I'm concerned about being overwhelmed with them. Also, how do they typically enter a tank - is it just likely they were on the LR?

Thanks a TON for all your help!

John

[rshimek]

Hi John,

Well, these are not moon jellys. The polyps are immortal, they will last as long as there is food providing they don't get a disease, get eaten or have some other malady occur. I don't think anybody really knows how many medusae these can bud off per given time period. My guess, if they are well fed, maybe dozens per year. The medusae are small, about the size of thimbles (hence the common name thimble jellies), but they are occasionally REALLY abundant. I have never been diving in the tropics when I didn't encounter at least a few, so I think they may be able to bud all year long.

They undoubtedly hitchhiked in live rock. I think these are very neat critters, with a capital NEAT, so I hope they do all right for you. :thumbsup:

[Telgian]

Thanks for the ID.
Now I have a name for another type of critter in my tank.
Here I've been thinking that they were a 'benign' type of hydroid.

I have a couple of small patches of these guys that have come into my tank on live rock as hitchikers.
They haven't been prolific in my tank, not in the way that the Cassiopea polyps are.

The first batch came into my tank on a rock with 'regular feather dusters' (and big fat cassiopea polyps).

[jgreen1025]

The medusae are small, about the size of thimbles (hence the common name thimble jellies), but they are occasionally REALLY abundant...

I think these are very neat critters, with a capital NEAT, so I hope they do all right for you. :thumbsup:

Thimble-sized, huh? Before I moved my tank last winter I had some tiny pinhead-sized jellies in there, but thimble-sized would be way more cool! I'm looking forward to seeing some of them bud off (it's all the extra little critters that make it so interesting). Any chance of harm to the fish or corals if they become "REALLY abundant?" How likely is it that they'll be getting chopped up by the powerheads, and would that foul the water much? And what do they eat?

John

[BeanAnimal]

I have a rock with piles of these.... even noticed a few on the other side of the tank. No decent macro lens for the digital... and not prepeared to buy the ogles yet....

Bean

[rshimek]

Hi John,

"Thimble-sized" is their adult size, so they would start out smaller. If they became really abundant they could definately harm corals or fishes. The odds are that they will not last a long time, as they will get "blenderized" by the powerheads. If you would want to keep them, you probably would have to raise them in an separate tank.

My guess is that they would initially appear as jellyfish about 1/4 the size of pencil erasers. If fed a lot of "meaty" plankton, such as live brine shrimp, they probably grow pretty fast.

[BeanAnimal]

I am confused here.... they seem to be attached? DO they "let go" and "swim" around after they mature?

DOH i just re-read "bud off"

Okay!

[Runner]

I have the same thing in my tank. I only identified them last week from a picture in a Sprung and Delbeek book (The Reef Aquarium, Volume II, Page 431). They started in a small location 3 years ago and gradually spread. Tubes that were active 3 years ago seem to still be active today. Two rocks are entirely covered and many others have growths on them. It seems that they don't initially grab on to areas with lots of coraline algae, but will eventually spread over those areas.

As for harm, I have see the tentacles cause an SPS to retreat from their sting. I have gotten itches up and down my arms two days ago from the stings as I tweezed some free in a water bucket. Then again, I have an LPS (a trumpet) that is about 2-1/2 years old and it doing fine in close proximity. The Nausithoe jellyfish won't grow up its stalk and the trumpet polyps expand fully -- even on top of the higher Nausithoe growths.

My biggest problem is that I can't seem to get zoanthids to open fully. I have tried many things and tested many things. I can only speculate that the medusa forms are annoying the zoanthids and keeping them from fully expanding. This has been going on about 6 months -- about the same time I had a population explosion of Nausithoe in my tank. Does it seem feasible that the jellyfish could be the culprit?

[rshimek]

Hi,

Just about anything is feasible.

From this disance, without seeing the tank, etc., it is impossible for me to say more. Sorry.

[Runner]

That's fine. I was just looking for something to blame it on. Before I discovered what these little guys were, I was blaming my pistol shrimp for no real good reason.
:)

[tangov559]

well, iv seen those in my tank too. I did a freshwater dip and they sucked in water and blew up. When i put the piece of rock back in my tank, my cleaners were eating them up. I thought that they were gone for good. But, its been a couple of days and they are coming back already. I dont know what to do. Any other ideas?

[romunov]

People have tried torching them, and they still returned.

[Runner]

Take the rock out of the water and spread kalk paste on them. Rinse with tank water after about a minute. I've wiped out colonies of these guys doing that. Of couse, it kills everything else on the rock and turns it totally white, but at least you can start over.

[jgreen1025]

Originally posted by Runner
Take the rock out of the water and spread kalk paste on them. Rinse with tank water after about a minute. I've wiped out colonies of these guys doing that. Of couse, it kills everything else on the rock and turns it totally white, but at least you can start over.

I don't understand - why is it necessary to kill them? I haven't seen them harm anything in my tank. Isn't having lots of diverse critters in a reef tank a "good" thing?

EDIT: Oops, sorry, I just read your post above where you said they were bothering your SPS corals.

John

[Runner]

Not only that, but they take over areas that prevent me from planting zoanthids (which are doing great now). They hydroids cover rocks and make them look like big, fuzzy balls if they are not contained. A few I wouldn't mind -- I'd enjoy them like I do my feather dusters. But I tried ignoring them for a long time and have lost control of a few rocks. War has been declared. ;)

One of my latest passive controls tried is that I have put a galaxea "upstream" from a clump of hydroids. Once it gets big enough to put out some long sweepers, we'll see who wins that battle. :)