Some 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.
Unlike 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!