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FAQs about Limpet Snails, Acmaeidae, Fissurellidae and more, Scutus, Stomatella

Related Articles: GastropodsSea SlugsMollusksAbalone

Related FAQs: Limpets 1, Limpets 2, Limpets 3, Limpets 4, & Limpet ID 2, Limpet Behavior, Limpet Compatibility, Limpet Selection, Limpet Systems, Limpet Feeding, Limpet Disease, Limpet Reproduction, & Marine Snails 1Marine Snails 2Marine Snails 3, Marine Snails 4, Snail ID 1, Snail ID 2, Snail Behavior, Snail Selection, Snail Compatibility, Snail Systems, Snail Feeding, Snail Disease, Snail Reproduction, MollusksSea SlugsAbalone

Mystery visitor, ID Stomatella Snail - 02/11/2007 Hi, <Hi Sean, Mich with you today.> Ok, first the flattery - the Conscientious Marine Aquarist has been a huge help to me in getting started in this completely addictive, humbling, and bankrupting hobby <Hehee!> and I've just bought Reef Invertebrates (online from the US, delivered to a friend of mine in the US because they won't deliver to Canada, and its not available anywhere up here!) <Oh NO!> Can't wait to find out when you are going to be putting out additional volumes. Any hints? <If I tell you, I'd have to kill you.> Second, I noticed a snail that I have not seen before in my tank (see attached), and while he seems to be harmless enough, I thought I'd better check. Is this a Stomatellid? <Yes!  A happy addition!> My tank is a 46g, going on about 2.5 years old, with live rock, a couple of clowns, 1 evil "other-fish-hating" <Hehee!> Blue Devil Damsel, and some crabs. As my tank matures, is the chance of new members to the community just popping up something to be expected? <Happens!> Thanks! <Welcome!  -Mich> Stouffville, ON

Is this a snail? ID Stomatella Snails, Cont'd - 02/11/2007 You guys do a great service to all of us hobbyists.   <Glad you think so!  Thanks!> Quick question, from these pics do these little guys look like snails?   <Yes, they are Stomatella Snails.  Lucky you!  A happy addition!> They are white, with what looks like a half shell on their backs, but doesn't nearly cover there whole body.  They also move very fast (20 inches in less than 30 seconds.)  They have appeared in ,add quantity, (probably around 30-40 of them in my 55 gallon tank)   Are they good to have?   <Yes!> Will they bother anything? <No!  Hopefully they will continue to reproduce in your tank!> Thanks again guys!!!! <Welcome!  -Mich>
The Incredible (Mr.) Limpet   2/24/06 I've recently noticed this small oval something in my 55 gal reef tank.  It is green in color and comes to a point in the center, almost like a mountain.  It typically stays in the same spot, but I recently noticed it moving about.  I've looked over your website to try to find something that looks similar, but no luck. Any help would be appreciated. <An archaeogastropod... of benefit. Bob Fenner>

Snail ID - 3/27/07 Hello everyone. <Hey Elaine, JustinN with you today.>   Can you please tell me what this is? <I'll give it a shot, for sure!> Sorry the photo's are not good I am new to cameras. <No worries> I found this thing in my small cube reef tank. I have attached quite a few photos because he looks so different in shape in 1 photo to another. Only way to describe him is he looks like a slug with a hump and 2 antennas. On 1 photo he looks like a torpedo shape but on the other he seems to have a slug looking appearance. He is quite rough looking and stone in colour with a hint of green on his back. Is he safe to leave in my reef tank or dose he need to go?   If he is safe what do I feed him on? Any advice is much appreciated thanks for your time.   Elaine <Say hello to your new Stomatella varia snail, my friend! These are very common hitchhikers on live rock, beneficial detritivores, happily munching away on your wastes and algae! No supplemental feeding is necessary, nor concern. He will be a perfect citizen, and may even produce a few more friends! -JustinN>

Re: Snail ID 3/27/07 Justin thanks ever so much for the reply I am so glad he can stay. By the way I think I have 3  of them so hopefully they can all become buddies. now I can get back to enjoying watching my tank instead of worrying about these things. Ugly though they are.   Thanks again Elaine <Anytime, Elaine. This is what we're here for, and we're glad to help! -JustinN>
Flatworm or Nudibranch? I.D. please I posted this guy after I found him clinging to the underside of my hammer coral. He's about an inch or so long, 1/2 an inch wide, and about 4-5 mm thick. I've looked on the net and books for an I.D. but thought maybe you guys could help out. Here's a link to where I posted a pic of this fella. Thanks, Mike <Mmm, is a Stomatella... a beneficial mollusk... as others have already pointed out. Bob Fenner>

Over Population of Unknown Origins  9/28/05 Bob, <Mark> I've been looking thru the FAQ's and Articles for a "snail" that is basically multiplying like rabbits in my tank. <Surprised you missed this one> I've attached a photograph, albeit a poor one, of one of these things.  I've been unable to find anything close to this on the site.  They seem harmless and are eating algae and the "gunk" on the glass.  It appears to have a shell but it's not like a "normal" snail.  I looked at the slugs and this doesn't fit there either. It may be some sort of abalone but it didn't quite fit the description or pictures here either.  Not really sure what to make of it but it really reproduces fast.  I have hundreds of the little guys in my tank and a couple of big ones (assume mom and dad).  The largest is probably a 3/4" long and they are brown with a mostly brown shell. <Looks like a Stomatellid to me... plug this family name into Google/WWM> They really seem to be exploding in population while my tank goes fallow. I'm trying to slay Crypt the dragon. <Heee!>   I'm winning the battle slowly.  I don't think that any of the fish I have were keeping the population down. I think these guys were in the live rock and were so small I didn't see them until they got big.  LR was labeled Marshall Island at the LFS.  It's beautiful rock with lots of purple and red in it.  There were only 2 of the little buggers so I didn't really think anything of it.  They were kind of cool to watch.  Several months later and there are hundreds of little ones. At some point the population boom has to slow down or I'm going to have to start removing them. <Likely you can sell them!> I know you will know what they are.  I'm sure they are very common if I've got em.  They sure don't look very exotic. Mark <Are useful algae eaters... about as "reef safe" as gastropods come. Bob Fenner>

Re: Over Population of Unknown Origins Bob, <Mark> Thanks for the reply.  The difficulty in finding something like this is not being smart enough to know where to start.  Even after having the starting point of Stomatella It took a bit to find the matching picture  Found it here, http://www.wetwebmedia.com/snailidfaq5.htm.   I was looking in the wrong spot before.  This is a very good match to what I have but the one in this picture is better looking, better color. <Yes> Sell them, now you're talkin.  How much are these things worth?  I'll have to ask the LFS If they want any. <Mmm, I'd look about locally... take some to your bigger shops that are privately owned/managed... and to the fish clubs... trade will get you far more than cash sales...> Thanks again, mystery solved Mark <Welcome. Bob Fenner>

Mollusk ID - Limpet 1/7/03  Hi Guys and Gals,  <Whassup G-money?>  This thing appeared the other day from my live rock. It's like a white hovercraft with a blowhole in the center.  <its a keyhole limpet (Mollusk... "snail" so to speak)>  I was thinking some kind of worm maybe, but really don't have a clue.  <false on the former, true on the latter <G>>  It is not very flat. Read through Reef Invertebrates, but nothing looked similar.  <look again my friend... page 202, the pic labeled Acmaea. Then look to the text for info on Limpets>  It's about 3/4" long. Any guesses?  <limpets are relatively harmless although not entirely reef safe (may eat coralline algae... other desirable benthic growths... sometimes coral tissue>  Thanks, and thinks for all the terrific help you guys provide. Jim P.  <with kind regards, Anthony> 

ID Snail/Slug ?? (with pictures) 4/6/04  Hello crew, These two guys came with two soft corals I recently picked up. I noticed them just before putting the pieces in my tank so I took them off and have been trying to figure out if they are friend or foe. My tank has all soft corals (polyps, pulsing xenia, zoos etc)  <Good to be cautious! Unknown hitch hikers are a good reason to quarantine.>  One has a green "hump"/shell on his back and the other has a hump but it is not as green. Another one was able to get in my tank and I have yet to find him/her.  <Your pic is a bit fuzzy, but the critter is almost certainly Stomatella Varia (AKA "cap snail"). If you do a Google search, you should be able to find a very good pic to compare to.> Good or Bad?  <One of the very best critters to have in your tank, IMO. They are nighttime algae grazers, harmless to all other animals in in many tank they are prolific spawners that provide a lot of coral food.>  Thanks again for all your help.  <It's always a pleasure!>

Orange Frilly Limpet - Lucapina aegis Can you ID this? <yep> It's in a reef tank. Is it bad or good , Friend or foe.. <foe... as most limpets ultimately are. They are somewhat indiscriminate feeders on benthic life forms. The brighter colors are usually a giveaway (noxious and freely predating on desirable reef life - perhaps corals or sponges). Its best to remove this species and a tank without reef invertebrates. Best regards, Anthony>

Unknown Critter 12/9/03 Hey there crew I got a problem here. about a month ago I noticed a odd looking creature on my LR. It is a snail like creature, it has a half shell on its back which is pink and white, it moves pretty fast moving around like a slug, <sounds like a Stomatellid... harmless as we know> now the weird part is its feeding mechanism, it looks just like a elephants trunk it feeds just like a vacuum cleaner its trunk is attached to the rock with another type of mechanism going up and down inside the trunk. <hmmm... perhaps not a Stomatellid if it has a proboscis> The shell is very small compared to the body which when it is on the move is almost a inch and a half in length. I wasn't to concerned until as of late because now it is growing pretty quickly and spots of my coralline are bare (not bleached) I believe it is eating the coralline because the patches that are missing are circular in appearance. <not the case here... a proboscis on a snail/gastropod is not "designed" to rasp coralline algae... instead look for another grazer (limpet, urchin) with short sturdy mouthparts (radula) to do this job> I will attach a couple pics of the monster if you could please identify him and if I should remove him or be looking for another culprit. <Yikes... these pics or over 5K kb and clogging our mailbox, mate. What's worse is that they are not clear at all. Please do resize all pics to small web-sized images (a few tens to a mere couple hundred kb max) and also please fill the frame with the subject (the snail is tiny here)> The other tank mates include 3 pepp shimp,1 Blood red cleaner,15 or so blue leg hermits,3 star shell snails and 10-15 Nass. snails. The only corals in the tank are a small frag of xenia and a small frogspawn which incidentally just started shrinking and spit out some brownish material (should I be concerned about this) <could simply be digestion or (worse) zooxanthellae expulsion if stressed> also a small false percula clown. One last thing I believe I spotted a mantis shrimp also I was feeding on day and a very small shrimp came flying out of a small piece of grape macro and snatched a piece of flake. He was brown in color and appeared to look a lot like a mantis shrimp. <most mantis are small smasher species and are fairly harmless... some do not exceed 1" by much as adults and are very harmless in fact. Please read through our archives/Reef Invert book to learn the diffs between smashers and spearers and species IDs> Well sorry for the book I wrote here but your help would be greatly appreciated. Thanks Jeremy from buffalo <wish I could have been more help... do send a better pic if you can. Best regards, Anthony>

Limpets Hi everyone , I have a tank full of small copepods that I know are beneficial. <indeed... I myself am Cuckoo for Copepods> But , and their is always a but, I have an unknown crustacean that I want to try to identify . <his name is Joey... Joey bag-O-doughnuts> This thing has a hard outer shell that looks like the hats that the Vietnamese people wear , almost to the letter . <a "Limpet" species... do use that name in a keyword search of the web... few pics posted yet on WWM of this critter. Common though> They are oval in shape , about a quarter inch in length ,have a white coloring and look like a pointed hat . Any ideas ? P.S.  Sorry about the ethnic description , but its the only thing I could think of that looked like these things . My LFS said they were Lipids Rich <no worries... understood and clear. And I don't think Vietnam will be calling for an apology... they love those little hats too. Your silly little "snail" is a Limpet dude. Best regards, Anthony>

Unknown Snail? Hi Bob and Gang, I browse your web site regularly and I find it very informative. I was wondering if you could tell me what kind of snail (I think) this is? Is it harmful to anything? <No> What does it eat? <Microalgae and life associated with them> Should I leave it in my tank? <Yes> Thanks, John ps. You Can use these pictures if you want to. <Thank you. This is some sort of limpet (as in the incredible Mr.), an Archaeogastropods mollusk. Please see WetWebMedia.com (the Google search tool on the homepage) re. Bob Fenner>

Nemo-aka the Blue Tang, and Gary the Stomatella Howdy again, fellow Wetheads!   I have a healthy, one-year-old 20-gallon reef tank into which I will introduce (after quarantine) a small juvenile Regal/Pacific Blue Tang (yes, my kids insisted on their own "Dory" fish after seeing previews of "Finding Nemo"). I've been studying up on the Blue Tang's weaknesses, such as Ick, and hazards (tailhooks!), and I feel ready for the new arrival.<good to hear>   The tank's inhabitants (2 little clownfish, a ravenous but friendly Royal Pseudochromis, candy-cane coral, a few small brown/green mushrooms, some Montipora digitata, many scarlet hermits, Astraea+Cerith+Nassarius+Trochus snails, copepods, small worms, mucho coralline algae, LR+LS, etc) will relocate with the Tang into a planned 60-gallon tank very soon,<this tang will need this tank soon :)> and when the Tang acts cramped in the 60-gallon, we'll start an even larger tank.<good> Meanwhile I need to modify the ecosystem in the existing 20-gallon tank so that tang-edible macroalgae has a better chance at growing "a little," while not overwhelming the corals and coralline algae.<agreed>   Obviously, I'm only counting on the tank itself to provide a tiny portion of the Tang's algae diet, but I'd like to have him/her at least enjoy a little more macroalgae decor to nibble upon between real meals. I plan to return a few of my larger snails to the Local Fish Store. -- First question - Does this Tang REALLY eat "bubble algae" (esp. Valonia)?<have never seen this species eat bubble algae...and haven't read about it either> Since I've sworn off bubble-munching Mithrax crabs (too omnidestructive), I'd love for the Tang to relieve me of my occasional bubble-scratching responsibilities.<will probably not eat bubble algae> -- Second question - Is there anything which conveniently dines on the STOMAT ELLA VARIA (sporty little half-snails!),<well I was thinking more towards a wrasse from the genus Pseudocheilinus, I know they eat can/will eat hermit crabs-but they might eat helpful creatures as well> which have been a very helpful ally against algae in my tank but now are too numerous (and keep everything so clean that the larger algae-seeking snails suffer)? This landscape will seem too barren to the Tang. But my instinct is that any carnivore nasty enough to eat Stoma Ella might also attack....corals? fish? my fingers? My hope is that you folks know of a cute, tiny, highly-specialized mantis shrimp (can I ask for iridescent-red?) or whatever that chews Stoma Ella yet eschews other stuff. Fantasy, right? <A mantis shrimp will eventually consume ALL of your small fish and your little crustaceans/snails too>   By the way, one additional REALLY irritating aspect of having Stomatella in your tank is that their low-rider bodies occasionally find their way through even the narrow slots in pump-intakes; the sound made by Stomatellids "paper shells" when they suddenly seize up a miniature pump impeller is "schwing" (as in the movie "Wayne's World"). Easy to fix but a pain.   Concerning Stomatella, I found questions by "C" from Pittsburgh, PA, (and Anthony Calfo's answers) in.... http://www.wetwebmedia.com/algcontfaq3.htm   ....and I'd like to reinforce Anthony's comment about this creature's "highly variable color." I started with maybe 3 or 4 TINY Stomatella (LR hitchhikers), soon had a population boom which subsided, and now there's seven or eight color/pattern variations, each apparently tuned to different LR surroundings. Not exactly crowd-pleasers, but they zip around like crazy, especially when the lights go out. On that note, goodnight and MANY thanks!<your welcome, I really don't believe there is a fish that specializes on Stoma Ella so it would be risking the lives of the other invertebrates in your aquarium, IanB> Bruce Mewhinney

Stomatella Questions Ah, the reference I had read about Tangs eating(?) bubble algae was in a WWM page....<well have been around this species of fish for about 5 years now and have never seen them even touch bubble algae, Bob has been around these fish longer so he might be right.> http://www.wetwebmedia.com/tangfaqs.htm   ....in which Bob Fenner replies to a reader ("Tangs Eating Bubble Algae"). Having said that, I haven't seen my newly-arrived Pacific Blue Tang touching MY bubble algae yet (I'm patient). But he/she is already happily chowing on sprigs of Red Gracilaria algae on a suction-cup clip; also flake algae etc.<normal for them to eat macro algae (softer easier to pick on, etc, bubble algae is to hard for one of those little 1-2" hippo tangs to eat> Back on topic -- Regarding possible predators upon the Stomatella varia snails, I did some subsequent search-engine sleuthing and came up with a few specifics....http://www.mindspear.com/reef/detrivore.htm    ["cleaner shrimp" eating smaller Stomatella?]<re: my other email> http://www.reeflounge.com/forum/viewtopic.php?p=4267    [peppermint shrimp "cleaned out" tankful of Stomatella]<maybe you should try them> For now I'm going to try peppermint shrimp (not banded coral shrimp), and in future maybe a few of the wrasses as you suggest, or even arrow crabs (in a much larger tank).<good luck with Stomatella control, IanB> Thanks again for help! Bruce Mewhinney

Snail id: Stomatella species "Paper Shell snail" 6/11/03 Howdy oh Wet ones! <not touching that one with a ten foot pole> I have found a bunch of snails in my tank, a type I have never seen before.  I have not be able to get a good picture of one yet, but I will describe it to you to see if it rings any bells.  It really looks like a land based slug, about 3/4 inch for the biggest one, maybe a little less.  It is a light speckled sandy color.  The strange thing about it is that the shell is only about 1/3 the length of the whole slug looking body, and it matches the body color and pattern pretty closely, so it was hard to even see the shell.  It is a rather flat shell, almost like an abalone shell.   <the last observation is the giveaway... you have a Stomatella snail species. Do use that genus name for a better web search. They are wonderful algae grazing snails... as harmless and reef-safe as it gets> It really looks like it has a great big tail because the shell is so small.  Now looking through the WWM site, I did not see any pictures of a snail that resembles it.  Does it sound like anything you have heard of or seen before?  I just want to make sure it is not a problem.  It cruises around the live rock like any other snail, but ya never no.... Thanks, Paul <just enjoy them and watch that S car Go! Kindly, Anthony

Black limpet snail- Scutus sp Hi:  I wonder if you can help me with identification of this new creature in my reef.  The reef is a year old but new things keep popping up.  This guy looks like a leach but is about 4 inches in length and about 2 inches wide and relatively flat.  He comes out at night.  The picture is of poor quality but may help.  He is black and has "frilly" edges.  I blasted him with a gush of water from the turkey baster and he slid back into the reef, so he isn't very shy.  Is he harmless?  Thanks, Jim <your creature is a mollusk of the genus Scutus (almost started to sound like  Dr. Seuss rhyme with the alliteration of 3 of the last 5 words <G>). AKA Black Limpet, is a mostly desirable snail. It may nibble on coral (of course, so do tangs and dwarf angels), but is an otherwise excellent algae eater and breeds well in captivity. Perfect for soft coral tanks... less so for LPS coral displays. Best regards, Anthony>

Accidental mollusk  Hi Bob,  Thanks for the answers to my previous questions.  Today during my weekly maintenance I noticed somebody new and was wondering if he's bad news. It is some sort of brown slug, 23 mm long, with a 12 mm shell on his head. It is the kind of shell I've seen thousands of times on Southern California beaches but always thought it was one half of a little clam. It is a shallow (almost flat) triangular shape shell. He was chewing around the base of some Halimeda and squirting out clouds of white from his mouth area several times for no apparent reason.  I have him sequestered in my quarantine tank until I hear from you. Should he stay or should he go? I am planning to add one or two "beginner" soft corals in the near future if that matters.  Thanks,  Brian Battles <I say "stay"... almost feel like a latter day Caesar with my thumb up! This is likely some sort of Limpet (as in the Incredible Mr.), and I know what you mean re the many Acmaea along the coast (I live in San Diego)... these are very beneficial creatures to have in a reef tank... are microphagous herbivores that greatly aid in filamentous/pest algae control. Count yourself lucky and enjoy it/hopefully "them". Bob Fenner, By Bob Fenner, www.wetwebmedia.com>

Scutus antipodes For the past 6 months I have been searching for the identity of a sea slug that piggy-backed on some live Fiji rock. I think I now know what he is: Scutus antipodes. Since I spotted the first one I now have 3 and they are an amazing critter to watch! Check out the attached pictures that I borrowed from another site. <Very nice> They seem reef safe, are they algae eaters? <Yes... and can grow to 15 cm... six inches!> Thanks,
<Bob Fenner>

Borrowed pix...

Snail-like creature ID: Limpet  12/3/08
<Hello, Lynn here this evening.>
I looked for these, I really did, but no luck. So I turn to you.
<Okie dokey>
These act like aquarium snails. From the bottom, they even look like them. From the top, though...not really. They look like little cones. Recognize 'em?
<Yep. They appear to be Limpets of some sort, and more than likely harmless grazers. Please see the following links for more information: http://www.wetwebmedia.com/gastropo.htm
Several FAQs at this page re: http://www.wetwebmedia.com/mollusca1.htm  >
Feel free to use the images if they are useful to you. It's the least I can do for your help.
<Thank you very much! Take care, Lynn>

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