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FAQs on the Hydrozoan Identification 1

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

Related FAQs: Hydrozoan ID 2, Hydrozoan ID 3, Hydrozoan ID 4, Hydrozoan ID 5, Hydrozoan ID 6, Hydrozoan ID 7, Hydrozoan ID 8, & Hydrozoans 1, Hydrozoans 2, 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

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)>

Lettuce sponge with feathers? Hi Bob! <Hello there> I have searched and searched through this web site but could not find anything similar to this problem... I have had an orange lettuce sponge in my reef tank for about 3 months now. It has been doing fine, but a few weeks after I got it, I started noticing a red feathery type of growth on it. The "feathers" continue to spread and grow larger, and I have no idea what this is. Is it a type of harmful algae, or just a natural part of this sponge? A turbo snail wandered onto it once and ate most of it off, but it just grew back. Any ideas? <Likely some type of hydroid. See here: http://www.wetwebmedia.com/cnidaria.htm  I might leave all alone... but am inclined to mention that if your sponge seems to be suffering from this growth, I might "snip" it off... with sharp scissors... with part of the sponge where it's attached... and siphon/vacuum out as much of the material as you can after. Bob Fenner> Laura

"Who was that masked man?" [Cnidarian ID] Right below the arm of the Atlantic gorgonian octocoral are some very fine anemone-looking creatures.  I'm not sure if you can tell from the picture, but they do not appear to be Aiptasia.  Instead, it looks like they are growing from very fine tubes.  In any event, it looks as if they are causing the polyps on the octocoral to retract.  Are these tube anemones?  Are they (otherwise) desirable? thanks tom <they are hydroids, Tom... a great nuisance... prolific and will burn many desirable corals and other creatures. Manually remove and be careful that overfeeding or messy feeding habits are not the cause of their current or future growth. Best regards, Anthony>

Unidentified Critters... stranded hydroids 6/9/04 I have had a 30 gal reef tank for about a month now.  I have 45 pounds of live rock and 3 corals so far.  Also some snails, hermit crabs, a sand star and a blood shrimp.  No fish yet. I have been diligently checking chemical balances and everything seems on target.  In the past few days I've noticed some unusual critters appearing on the glass and live rock.  I've seen several very small snails (1/32 inch) which began appearing before I introduced snails into the tank, so I assume they've come from the LR. <yes... indeed> In the past week I've noticed several translucent critters on the glass which move like snails, have no shells, are about 1/8 inch long and have 2 points at their back end. <sounds like a flatworm... the little milky white ones prey on copepods. All are harmless> From reviewing other questions responses you've given, I've identified them as flat worms which are not harmful.   <Ah, BINGO- you win the hairy kewpie doll! Very glad to hear you in the archives :) > However yesterday I've noticed a new critter which, in reviewing your Q&A's, I cannot identify.  These seem to have emerged within the past day.  They appear to be long white strands with a single row of "hair" (1/16-1/8 inches long) on one side. (Almost like a 1 sided long skinny white feather.)   <Yikes... I recognize it already. It is a very distinct description. Your creature is a fiercely stinging hydroid. Do remove it... it will sting you and your animals alike> They seem to be about 2-4 inches long and appear to emerge from a jelly like polyp on the rock. They drift with the current from my power-head, and periodically retract back into the polyp.  I assume that they are "netting" micro-organisms, then "reeling them in" to be consumed. These strands are so thin that they are not visible unless you are very close to the glass.  Any idea what these things are?  Are they dangerous to the other life in the tank? <yes... do be careful. Best of luck, Anthony>

Ref: invert ref guide-j. sprung.  Myrionema/stinging hydroid. i was quite pleased with them until i found out they are pests. now i feel like i was bragging about a tank full of anemones! Aahh, oh well. all blissful ignorance must come to an end at some time. <Embrace the change. Bob Fenner>

Brown pom poms: hydroid ID 3/17/04 please identify these brown pom pom like polyps that are growing on my LR with my yellow stars. They are spreading and having a hard time getting rid of them. <they are the nuisance hydroid Myrionema and they can be a serious problem> I have been trying to rub them off with my fingers and they come back quickly. <Yikes! touch nothing in the tank with bare hands/fingers my friend! We have seen/written about (see archives) folks get seriously injured/ill this way. Piscine tuberculosis, Vibrio infections, etc> Please tell me the best way to get rid of them. See attached photo. thanks Ron <use the genus name provided above to do a keyword search of our archives (Google tool at bottom of our homepage) and beyond on the internet. Best regards, Anthony>

Bad boyz- hydroids 12/30/03 Hi guys <howdy> Can you please identify these "creatures", they are about a quarter of an inch long and have a "coil" at their base. I'm also not sure about the green bubbles. Are either of these a problem? <the tube-like critters are stinging hydroids and the bubbles are a Valonia type algae or Halicystis stage of Derbesia hair algae. All are pests. Do read through our archives of articles and FAQs for the (nutrient) control of such organisms> <best of luck my friend. Anthony>

Unknown animal, invertebrate, probably hydroid About myself: for the past twenty-five years I have been a developer of advanced performance materials and only recently started to maintain marine tanks. I have always been fascinated by the marine environment but in the past mostly enjoyed it from a canoe (frequently at night) on the Chesapeake Bay and the Albemarle Sound. <interesting... and are you a member of the excellent local aquarium society, CMAS? Do look them up.. great club.> About my tank: the tank in question is a refugium that I could never bring myself to hook up its main tank. It was too fascinating to risk ruining. It is 20 g with Inland Aquatics detritivore and refugium flora kits 20lbs live sand and 10lbs live rock (one piece) 2x65W 6500K PC lights, no filter or skimmer - just a single airstone. After Hurricane Isabel, it went 6 days without any lights or aeration (we had no power). Only obvious loss of life was one very small snail. Upon return of power there was a slight cloudiness that immediately cleared and was followed by a slowly worsening algal storm that grew day by day until visibility was only a few centimeters. Much of my macroalgae died and my copepods began to disappear. At the same time a new animal began to appear in increasing numbers. Here is a snapshot of it: <a Cnidarian... looks like/is likely to be a hydroid IMO> It was about 1 cm in diameter and appeared to me to be some kind of hydroid larva. <agreed... not uncommon> The algal storm finally cleared and simultaneously the mystery larva disappeared. I now have thriving copepod swarms and a goodish bit of Cyanobacteria on the substrate. <increase water flow and protein skimming to eradicate this Cyano> My son and I have looked hopefully for some polyps to appear. We are quite excited by the prospect of finding the adult animal. But so far we have not seen anything new. My question: What is the mystery larva? Where did it come from? Where has it gone? <about all I can say for sure is that larvae/medusae were likely carried in with some recent addition (water from a wild source, on the shells of Astraea snails, in bag water from another aquarium with shared livestock that was not (properly) quarantined by you, etc> What was its relation to the anoxic period, the algal storm and the copepod population changes? What kind of adult animal can we hope to find? and what should we look for? <time will reveal> I have feed the tank regularly with shrimp pellets waiting until previous offerings have disappeared. Right before the algal storm, and perhaps causing the storm, I fed with two Spirulina tablets that took weeks to disappear and only after they disappeared did the storm begin to clear. During the storm I did not feed because I was waiting for the tablets to be consumed. With such a heavy storm I felt that there was no lack of nutrients to worry about. After the storm cleared, I resumed feeding with shrimp pellets and weekly inoculations of DT. The water has since remained clear. I test regularly, but the water parameters are always perfect: Ca-400ppm, Total alkalinity-4.5meq/l. No measurable nitrate on a reliable nitrate test. <do allow some nitrites (5ppm) if you will keep corals successfully long term> Phosphate is low. I got these results even during the algal storm! I thought some mineral parameter must be off, but I guess that the nutrients must have been bound in organic molecules and not detected by the tests. Of all my tanks, this tank has, by far, the best test values. Also, there is no erosion of the live rock which I see in the other tanks even though I work hard to maintain calcium, magnesium and total alkalinity in those tanks. I have never needed to add any mineral supplement to this tank because the tests have always shown ideal values. (I suspect that the erosion of live rocks in the other tanks is associated with the use of calcium chloride in most calcium supplements. I have been experimenting widely with calcium supplements and I am not happy yet with anything that I have tried). <I strongly advise the daily use of calcium hydroxide with or without a calcium reactor. It is tried and try and has many benefits over other means of delivering calcium> I suspect that I tend and feed the tanks rather than the livestock. I don't have many fish: 7 in my 75 gallon and 2 in my 125 gallon. I am fascinated by the water and all the complex interactions between its inhabitants that it is my privilege to observe. I seldom intervene in the tanks except to try to provide stable conditions, light and a modicum of food. I am very interested in the zooplankton populations and have been toying with the idea of harvesting plankton from the Chesapeake Bay and adding them to one of my tanks. At night, when I go canoeing, that are beautiful displays of phosphorescent plankton and medusa. <yes... a marvel> I encounter them in small patches. Some patches are blue and some are green and seem to phosphoresce in response to being disturbed by the canoe. I would love to capture some of these and see what happens when they are placed in a tank. It is probably a crazy idea. <some are toxic as you may know... do be careful here> I don't know what animals I would be introducing, what their life-cycle would be, or what impact it could have on my tank. I would appreciate any warnings or suggestions for reducing risk that you might care to share. <all can/will be screened by the proper use of quarantine tanks for all things wet coming in... corals, fishes, snails, algae, live rock, etc... everything please> Thanks for your attention. I have really enjoyed reading the articles and FAQs. They seem very factual and have proven quite reliable. Karl <thanks kindly... wishing you the best. Anthony><<RMF lost the pic... pls re-send if you see this. Bob>>

Brown Hydroid Myrionema 11/17/03 Hi! I was wondering if you could tell me what is growing on this rock with my yellow Stars? See attached photo. <it is a fairly common nuisance hydroid, Myrionema... somewhat handsome looking to me, but is admittedly a problem... can be a plague. They will sting corals and clams and are invasive as you have noticed> They are spreading very fast. At first I thought they might the yellow stars just multiplying but they are brownish in color instead of yellow. Please let me know what you think. thanks Anj <alas, we are not aware of anything that consumes them yet (surely some organism(s) does/do). Manual extraction will be necessary and be mindful of not overfeeding the display which can fuel their growth. Anthony>

Hydroid hitchhikers 7/15/03 Thanks Anthony. The crab in question finally came out of the rock work again and I fished him out to take a closer look. Since I have the option, what do you recommend, keep hydroids out of the tank or put them back in? <in a big enough reef tank, I'd leave them in. Good water quality and they are unlikely to flourish> The ones on that crab seem to be the only colony. As for Aiptasia, I have had three very small ones that I first noticed about a month ago. They haven't got much bigger in that time and they certainly have not increased to plague proportions as I have read others report. < a good sign indeed. A well managed aquarium can have them in the display for years with little reproduction. Its all about nutrient control> However, I am almost to the point where I want to start stocking with inverts in earnest. Shall I remove rock and nuke them while I still have the chance or is good water quality enough to avoid problems later? <its enough... but then again, most people overfeed or overstock in time. Do remove the Aiptasia to play it safe. And be sure to QT all new inverts, rock, sand in the future to prevent such critters from coming into the display> By the way, my LFS has several rather large Aiptasia in their tanks. Should one always avoid buying out of tanks like that? <heck no! good husbandry means QT at home. You can screen most anything from there.> Finally, if you would be so kind as to offer a personal opinion. In general, would you expect the dual 6" skimmers driven with Rio 600RV's found on the CPR CY294 to do the job for a 170 gallon tank? <I think CPR skimmers can be tuned to work very well... but are not so low maintenance or effective as EuroReef's (idiot-proof and excellent). Aqua C skimmers instead are one of the very best values. Two I would put ahead of CPR skimmers> I expect to focus on inverts and lightly stock with fish. After running the tank for 2 months and with only a couple of LPS and a half a dozen small fish (5 Blue-green Chromis and a Sailfin Tang) plus a full complement of snails and crabs, the skimmer throats are thoroughly coated every day but I get very little liquid in the collection cups. Is that what you would expect with a light bio-load or should I be trying to produce more skimmate even if it looks a little on the pale side. This is my first aquarium, and I have no reference point for comparison. Regards. <no worries. Best regards, Anthony>

Hermit crab hitchhikers: Hydroids - 7/14/03 What's this growing on the hermit crab's shell? Please don't tell me it's Aiptasia. <no worries.. or at least, they are not Aiptasia. They are hydroids... and quite a handsome colony at that. Yet - they can be fiercely stinging and no less formidable to other invertebrates as Aiptasia> I do have 3 Aiptasia in a new tank that I have just begun to stock, but they don't look like this. <no worries about your glass anemones either... they only flourish in tanks with nutrient control problems (poor skimming, poor water flow, overfeeding, etc)> The ones I know that are Aiptasia are0.25-0.5cm across, brown and look just like the pictures on your site. The ones in the attached photo are much smaller, clear and growing like shaggy hair on their transport. Thanks. <do enjoy them in the meantime... a fascinating creature and one that will behave if you maintain proper water quality. Anthony>

Myrionema... Brown Pom-Pom Hydrozoan 11/20/03 I sent you an email earlier with the wrong picture, sorry. Could you please identify what is growing with my yellow star polyps. They are more brownish than the yellow stars and seem to be spreading quickly. Thanks Anjanette <the organism pictured is unfortunately a nuisance Hydrozoan of the genus Myrionema. There are no clear predators on this creature to date that we are aware of... manual extraction is necessary. Also control nutrient that fuel it (skim well, do small frequent water changes, careful not to overfeed/overstock. Best regards, Anthony>

Cnidarian ID Myrionema - stinging hydroid 7/18/03 Hi Guys, <cheers> I have a very strange algae growth in my 50 gal reef tank (see enclosed pics). I think this stuff came in on some live rock I bought from a local reefer about a year ago. Now it is starting to take over my tank. <you have the nuisance hydroid Myrionema from the Pacific. It can sting and burn corals, clams, etc> I'm wondering if you know of anything to help me rid my tank of this stuff. <some limpets eat it> My parameters are: 50 gal reef (no sump) 4 x 96 watt PC lighting Remora Pro skimmer Approximately 65 - 75 lbs. live rock Deep Sand Bed 700 gph water movement (power heads) S.G 1.025 (refractometer) Temperature 79-82 F. Calcium 400 - 420 KH 7 pH 8.1 - 8.4 Ammonia/Nitrites 0 Nitrates 0 Water changes/top offs with RO/DI Thanks for any advice, Brian <some manual extraction may help as with a tooth brush tied to the end of a running siphon to scrub and suck the pest out without spreading it. Best regards, Anthony>

Digitate hydroids I have recently set up my first salt tank and purchased some live  rock.  I noticed that there was some strange come out of the live  rock.  I did an internet search and have found out I have at least two  Digitate Hydroids.  One completely disappears when the light comes on the  other is about a tenth of an inch long.  It is about three inches long with  the lights out the other is about an inch or two.  I have not been able to  find much information on these creatures.  I want to know if they are  safe. << Yes, I would keep them and not worry about them. >> I also need to get a moon light to see what I am missing. << A flashlight in the middle of the night comes in handy as well. >> Thanks, Ed <<  Blundell  >>  

Many thanks and ID question... First, let me say "thank you" for myself and all the others you have helped.  I've been reading and absorbing as much as I can from your site. <Ah, good> Some LR added to my tank has apparently been "dead rock" for over a month; it was a very small piece, and I bought it because I had thoughts of adding some zoos to it later.  It has been slowly coming to life, and recently sprouted a small colony of about 20 little thingies.  They are very tiny (~2-3mm tall) and look like a small wind turbine -- narrow stalk and four 'arms' in a cross at the top with small dots at the ends. <I see them... Hydrozoans of some sort> I've attached a picture, hoping that you can ID them. My apologies for the focus, but even in macro mode, they are tough to capture. Thanks again and warm regards, Matthew <A good enough pic. These can be troublesome creatures as a group... stinging you and your livestock... but generally they "cycle out" of their own accord in time. Please read here: http://www.wetwebmedia.com/hydrozoans.htm and the linked files (in blue, above) where you lead yourself. Bob Fenner>

Hydroids to Flatworms Hi Guys, I have a cluster of little brown pom-pom like things in my reef. Using the Google search on your site, I found out that they are "a fairly common nuisance hydroid, Myrionema". My question was answered. <Good> While I was on the Hydrozoans FAQ page I noticed a posting titled "Stranded Hydroid! Yikes! 4/7/05". Your staff answered the question and identified the animal as a hydroid. I had similar things in my tank growing on a finger leather coral. It turned out to be some kind of flatworm. It had the same tentacles in the posted picture. The worm would release the tentacle into the current and pull it back repeatedly. <Strange, interesting... have not heard of, seen this offered re flatworm behavior ever> The worms are very clear, so they almost disappear when they are spread out over the surface of the coral which makes it seem that the tentacle is coming from the coral itself. <Good plan, eh?> I used Salifert Flatworm Exit in a bag of tank water and dipped the coral in it. After approximately 45 minutes the flatworm came off by creating a current in the bag with my finger. It was a clear, slightly cloudy flatworm. Even sitting on the bottom of the bag, it released the tentacle and pulled it back. The tentacle was a long single strand which had smaller lines coming off one side. I actually got a few of them using the dip. Each worm only had one strand - so if you see more than one - chances are that there are several worms. Great Site. <Thank you for this input. Will try to find the bit you reference and couple it with yours here> Dave Here was the full post from the FAQ: 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>

Hydroids... Hydrozoan: what's in a name? 6/21/05 Ah, yes... understood. It really does look like a flatworm. Not so though. Its a ctenophore... benthic sort of "hydroid" or "jelly" (not the same, but kin). In the hobby... we have been calling the thing that I think you are seeing (a unique description... really sounds like it) "a hydroid" for lack of a better understanding/term. Pics of one of my own attached - its being scraped from the underside of a Fungiid. And... a link to a quick mention of the lil buggers here: http://www.seaslugforum.net/display.cfm?id=12274 Anthony :)

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