Home | Aquarium Livestock | What is that in my Aquarium? – Part 1 – Stomatella Snails

What is that in my Aquarium? – Part 1 – Stomatella Snails

Stomatella SnailSome of the most interesting animals in aquariums can be the ones we never knew we had.  Aquarists often turn to the internet in trying to figure out what some unidentified thing in their aquarium is and where it came from. One of my favorite unexpected hitchhikers is the Stomatella Snail.

Stomatella Snails look like and are often mistaken for several other organisms like Limpets, Nudibranchs (sea slugs), or Abalone Snails but they are actually more closely related to Turbo and Margarita Snails. Stomatella’s only grow to just over an inch in length and have a small, flat shell on the top of their body. They actually don’t fully withdraw into their shell like other more traditional snails. This external shell and small operculum (the “trapdoor”) on the back of their foot separate them from the Nudibranchs and sea slugs, and the lack of “holes” and openings in the shell separate them from the Limpets and Abalones.

Stomatella SnailUnlike many of the other hitchhikers and snails that appear in our tanks, Stomatella’s are reef safe. They are grazers and will feed on algae from the rockwork and on the glass. While they may reproduce in your tank, they usually don’t overrun the tank like some other nuisance critters might. These snails are usually dark brown or black, but can be almost any color – I’ve even seen some that are bright lime green. Stomatella’s are usually more active at night and you may be able to spot them if you shine a flashlight on your tank after the lights have gone out, but it isn’t unusual to see them cruising around on the glass or rocks at night.

So, while you may need to worry about some other hitchhikers that show up from your corals and live rock, these little grazers can be a blessing in disguise and a fun little (unexpected) addition to your saltwater tank!


  1. avatar

    This has been most helpful, thank you! I have spotted one of the little guys in our tank several times (after we turn the lights off and the moonlighting on) but he’s very elusive, as soon as you turn the light on again to get a better look he hauls butt back to a hiding spot in the live rock.

  2. avatar

    I have a tropical set up and I think it is these little creatures I have just seen. Are they harmfull to the tank.

  3. avatar

    Hello Paul, Is your tropical set up freshwater or saltwater? These snails are only found in saltwater aquariums and as mentioned, are not harmful.

  4. avatar

    Rattling instructive and good body structure of subject matter, now that’s
    user pleasant (:.

  5. avatar

    I just discovered one in my tank, a medium green little guy. I recently added a variety of plants to my saltwater tank, and I think he hitchhiked in on that. He’s a cute little bugger, and I hope he enjoys his new home.

  6. avatar

    We have a 55 gallon tank. I have counted at least 60 black stomatella. If they don’t become a nuisance, that’s good, but how many would too many be? It hitched hiked in on live rock. Started seeing one, then little ones and now last count was 60.

  7. avatar

    Hello Karen, There is no threshold to what is considered a nuisance. If it is too many for you or affecting your filtration or other systems, its a nuisance. If they don’t bother you, they aren’t.

  8. avatar

    I just noticed one in my tank I added more coral but small frags this little thing is pinkish though

About Eileen Daub

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Marine Biologist/Aquatic Husbandry Manager I was one of those kids who said "I want to be a marine biologist when I grow up!"....except then I actually became one. After a brief time at the United States Coast Guard Academy, I graduated from Coastal Carolina University in Myrtle Beach, South Carolina in 2004. Since then, I've been a marine biologist at That Fish Place - That Pet Place, along with a Fish Room supervisor, copywriter, livestock inventory controller, livestock mail-order supervisor and other duties here and there. I also spent eight seasons as a professional actress with the Pennsylvania Renaissance Faire and in other local roles. If that isn't bad enough, I'm a proud Crazy Hockey Fan (go Flyers and go Hershey Bears!).