Please visit our Sponsors
FAQs on the Hydrozoans 2

Related Articles: Hydrozoans 1, Cnidarians, Fire Corals, Stylasterines, Hydrozoan Jellies,

Related FAQs: Hydrozoans 1, Hydrozoan Identification, Hydrozoan Behavior, Hydrozoan Compatibility, Hydrozoan Selection, Hydrozoan Systems, Hydrozoan Feeding, Hydrozoan Disease, Hydrozoan Reproduction, Medusoids/Jellies (Ctenophores, some Hydrozoans, Scyphozoans): Jelly Identification, Jelly Behavior, Jelly Compatibility, Jelly Selection, Jelly Systems, Jelly Feeding, Jelly Disease, Jelly Reproduction, Fire Corals Lace Corals, Stinging-celled Animals

Some fishes are relatively immune to most Hydrozoan stings.

Hydroid ID and control       5/4/16
Hello WWM Crew,
I have noticed a great deal of what looks like some kind of stringy white algae growing in the darker, lower flow section of my large reef tank (under shelves and overhanging rocks, etc.).
<Mmm; no; these are Hydropolyps; not algae>
I didn’t think much of it, but I noticed recently that previously happy Zoanthid colonies are now staying closed most of the day, and longer spreading or fluorescing nearly as much as they should. It appears the two observations may be related, as I can see a few of these same stringy, branching, algae-looking structures extending up through the affected Zoanthid colonies. On closer inspection, I can see that the stringy hairy things have what looks like a feather duster fan or even a tentacled polyp. I’m starting to believe that they’re a type of hydroid, and am wondering if there’s anything I can do to stop them overtaking and killing my beloved Zoas.
<Sure: Read here: http://www.wetwebmedia.com/hyzoancompfaq.htm
Below is a photo of some of the culprits — I believe the span of the tentacles is less than 2mm, on average. I’d be grateful for any help in ID’ing the species,
<Mmm; see WWM re Hydrozoan ID>
as well as any suggestions you might have on how to reduce their proliferation.
<Welcome. Bob Fenner>

Variation in hydroids?    4/15/06 Good day WWM crew!  You folks the bomb! <Boom, boom da boom...> Sew, I noticed on ReefCentral, on their current (4-14-06) homepage, for their slideshow presentation, they have some images of hydroids mixed in there. <Are common in shallow reef environments...> I've had what I thought to be a rather small colony though spreading all over rockwork, of polyps.  They look like a mini version of snake polyps or a variation of a small yellow polyp.  I can provide images if needed. <Please do> My question, mainly.....these guys in my tank, that look almost identical to the slideshow on ReefCentral, retract when touched or if anything moves or swims by them.....so, are there any species of hydroids that retract? <Likely so> If so, I would have never known such....and am craving a definitive answer.  Thanks very much for your time, look forward to hearing from you. Hydroidy polyp. <Please read here: http://wetwebmedia.com/hydrozoans.htm and the linked FAQs file above. Bob Fenner>

Hydroid identification... no graphic  - 2/15/2006 Hey pros got a quick question for you.  I was browsing through your array of posts and articles when I stumbled upon the "Hydrozoan" section.  I looked through the photos and found one that is similar to something I have in my tank.  The picture I'm referring to is under a post entitled "Bad boyz hydroids- 12-30-03.  The picture shows small tube-like structures protruding from the live rock with tiny little white heads. <Covers many species...> I have something similar in my aquarium.  There are several small (1/16 to 1/8 on an inch) solid tubes, purple in color (covered in coralline algae) that appear to be growing out form the coralline algae (or maybe the coralline is just growing onto it). On the end is a tiny filamentous structure (looks like a clear bubble but it's very small so hard to tell) but in either case it looks as if it could pull inside the tude. <? Not retractable> These little tubes have been there for at least a few months if not year, I never paid attention to them, and I have never noticed them bother anything.  There are no corals growing near them, but I assuming if I see them in that spot then they are probably growing other places too. All corals (Shrooms, xenias, colt, zoos, and gorgonians) seem to be doing fine.  Can I do a test by placing a small xenia, perhaps, near this "hydroid" to see what happens?  Are these little tubes always "bad" or can they be beneficial/neutral creatures as well? <As long as "stay small", to themselves>   I have seen other similar creatures that live in tubes (some straight some coiled) that have feather duster like heads.  I'm certain these aren't harmful, but how do you visually separate these from hydroids?   <If trouble, best to remove, denude from the rock> One post stated that they can look like corals, algae, or jellyfish.  That describes many small creatures I see in my aquarium, how do I separate the good from the bad? Thank you Jon <... a photo or drawing please. Bob Fenner>

Little white pests...but not Aiptasia...and other problems Hi, hope you can help! <Will do my best> Background: We have a 125 gal saltwater tank with 2 filters, protein skimmer, but no reef lighting (yet). <... but some lighting?>   Inhabitants are a yellow tang, Firefish, coral beauty, 2 cleaner shrimp, a pink knobby Cuke, a dozen or so hermit crabs, and damsels.  (Neon damsel, blue damsel, humbug damsel, 3 green Chromis.)  We have several large live rocks, and a few pieces of fake decorator coral junk while we wait to get the right lighting to add the real stuff.  Substrate is a mix of live sand and crushed coral.  Chemistry and temp perfect.  Tank is about 6 mo.s established.  All is well in there. We have a 20 gal hospital tank for inductees and sick guys, currently only inhabited by 2 cleaner shrimp and a few hermits, about 4 months old.  A few pieces of decorator plastic caves, and a few pieces of live rock.  Same substrate.  Same chemistry and temp as 125 gal tank, but our new fish don't survive it'¦ not sure if something is wrong in there or if we are getting bad stock or what's going on.   <Good list of speculations... you are using your big tank's water there? I would> We don't want to introduce new fish into the big tank, because we've already experienced 'chasing down the sick guy' in the big tank, and it's not good for any of the other inhabitants. <Well-stated>   We had two lunare wrasses in the main tank for about a month that were trying to eat everyone else, so we moved them to the hospital tank for a few weeks before returning them to the pet store, and they were fine in there. <Interesting... gives weight to the "initial bunk livestock" theory> We feed with frozen multi-pack foods in the eve, and leave dried seaweed pieces pinned up during the day, both of which are eaten voraciously, but nobody looks to be starving, or even close, and the shrimp are molting and hermits moving to new homes, but no visible food decaying or spike in nitrates, so think we are good with feeding. Problem #1:  Every time we get new fish, they die in the hospital tank, usually within 3-5 days of arrival.  We do 10% water changes (in both tanks) every week.  We have tried a 100% water change in the hospital (several times).  We have tried restoring it with water from both the main tank and clean water source to help match. <Ah, I see>   (Water source is completely purified, we bought a water purification system solely for the tank water, and add Oceanic Salt.) <I would read over re synthetic salt mix brands... on WWM, the Net... and switch to something else (myself)>   Occasionally we see signs of ich on the new guys 'when we do, we remove the carbon in the filter and treat with Kick Ich'¦. <This product is worse than worthless. Please read here: http://www.wetwebmedia.com/homeopathfaqs.htm At best it's a misleading placebo, worse, it may be poisoning your system to a degree> but sometimes no signs of ich, they just keel over.  We used to induct our fish over a several hour period to the hospital tank, lights off, adding ¼ cup to their bags at a time until introducing, but have gone even farther now to a 'drip method' where we place the fish and water in a (covered, dark) container, and slowly drip the hospital tank water into the container until it overflows into a bucket (4-6 hours or so), before introducing the fish into the tank.  Still they die.  Any advice or thoughts??? <Lots... for here, try a Polyfilter in your water flow path... see if you "get any color"... You likely have a poison source here... perhaps a bit of metal from... a clamp? Ornament? Check with other hobbyists in your LFS/source store... do they have similar lack of "luck?"> Problem #2:  Several months ago we were thrilled to see a bunch of 'little white things' birthed in our 125 tank and floating around.  (Hey, stuff is living!!)  =)  They were free-swimming, with a tiny ring of tentacle looking things around the top, sort of hydra-looking, and may have been Aiptasia, <Nah... not this life's M.O.> but if so did not last long.  (Probably got eaten.)  About a month ago, there was a birthing of same in the hospital tank.  We had added some live rock, and also infused some water from main tank, so don't know source.  At the time there were (doomed) fish in there, so only one of the birthed critters survived.  He lodged himself on a shell and grew to be about an inch or two long!  He was white, with a large rotund belly, and a small hole at one end.   <Sounds like my ex-brother in-law> No visible tentacles, really, but a small circle of very short hair like things around its hole.  Interior appears almost hollow.  No narrow base, far removed from Aiptasia descriptions, obviously alive due to growth, but not movement, (stationary in all regards), and very ugly.  Sort of like an onion?  After another batch (3) of new fish died, we removed him as well, as we did not know what he was and he was therefore suspect. (About 3 weeks ago.) <Likely not related to your fish mortalities, and don't know what this is exactly... see below> Last week, there was another birthing of these things in the hospital tank! They appear first as free-floating creatures with little umbrella heads (very tiny), almost like hydras, but then affix themselves everywhere--the glass, heater, shells in the substrate, and commence to filling out with the wide belly onion look.   They are growing, and are now already probably 1/8-1/4 inch long.  I have searched and searched and can't determine what these things are.  They fit the description of Aiptasia in how they arrive and behave, but not at all in appearance after that. <Actually, not an Actinarian (anemone) but likely a hydroid of some sort... a guess based on your description of appearance and life history. Not desirable, but no reason to panic either... they are originating from a bit of live rock (strobilizing is the fancy word). They will "run out of eggs" someday soon.> Any help? <Oh yeah, getting to something in the way of a real solution... Here's the big wind-up and the pitch.... a refugium! I'd attach another (live) sump container to your existing system, put it on at least a reverse timed lighting schedule (do get some light for your main tank if you don't have this as well), and grow some live macro-algae, have a DSB there... Voila! Whatever the problems are/were, solved. Please read here: http://www.wetwebmedia.com/refugium.htm and the linked files above till you understand rubber band. Bob Fenner> Thanks,

Stranded Hydroid! Yikes! 4/7/05 Hello WWM Crew, <howdy> I have a quick question for you regarding a finger leather and a strange set of tentacles coming from it. <yikes! they are not from the leather, but instead are from a stinging hydroid. They can be quite aggressive to other reef creatures and even burn your skin painfully> I have attached a picture of  identical tentacles as what are coming from my leather but am unsure of how to deal with this issue. <manual removal> I have only had the leather for 3 weeks now and it has never extended a single polyp. <Perhaps it's irritated from the hydroid. More importantly... I fear you have added this coral to your tank without a proper quarantine period. Yikes, if so... it's a surefire way to introduce pests and predators to your tank like this hydroid> Every evening these threads come out and they are very intricate which is what led me to believe they were not just mucous. I cannot see anything on the leather itself  by following the threads but there are 6 or 7 coming out. Any help you can give me would be greatly appreciated. Regards, Scott B. <There are many types of hydroids in the world. Some look like corals... some look like algae... others more like jellyfish. Caution with all :) Anthony>

Strange Little Creature Hi All I have recently setup a marine aquarium and spent a lot of time researching the do's and don'ts! I have a 250L aquarium with Eheim Wet/Dry Filter, Red Sea Turbo Skimmer, and Internal Jewel Mechanical/Chemical Filter (which I want to replace for an external). The tank currently holds 30Kgs of uncured live rock which over the last 4 weeks has gone from looking quite sad to very happy indeed! and a further 20kgs of crushed CaribSea sand and shells. I still have a few weeks to go though before any livestock can go in but my ammonia is 0 and my nitrate is now 0.3mg/l. There are lots of critters which I have been able to identify but one in particular has got me, please could you see if you know what he is? He is living on the glass amongst the diatoms which have started to appear everywhere, should these diatoms be left alone until I put a cleanup crew in?  <I would clean the diatoms off the glass. That creature could possibly be a hydroid, something you really don't want in the tank. To be safe, I'd squish him. James (Salty Dog)>

Become a Sponsor Features:
Daily FAQs FW Daily FAQs SW Pix of the Day FW Pix of the Day New On WWM
Helpful Links Hobbyist Forum Calendars Admin Index Cover Images
Featured Sponsors: