An inquiry came in (with the subject line: urgent snail question) asking, “How big is the biggest snail you’ve ever seen?” Thinking that others might be interested, here is my answer.
The largest snail? There could be many ways of answering that question. Size could refer to length, diameter, volume, or mass. The longest mollusk I have seen is the giant squid on display at the Smithsonian, but that is a cephalopod, not a snail, and it doesn’t have a shell. The largest shell I have seen is a fossil ammonite that was more than 2 meters in diameter, but that is also a cephalopod, not a snail, and maybe fossils are not acceptable for this answer.
The largest modern shell I have seen is that of a giant clam, but that is a bivalve, not a snail. The largest bona fide snail I have seen could be the snail in the Dr. Dolittle movie that carried Dr. Dolittle under the sea, but movies don’t always depict reality (sorry), so maybe that one doesn’t count. Another large snail I read about is a fossil sea snail from the Eocene Epoch (34-56 million years ago) called Campanile giganteum, which grew up to 1 meter long (Houbrick, 1984). But I haven’t actually seen one, which is really what you asked, and maybe you don’t want to include fossils.
Real answers start here. I would have to say the largest modern snail shell I have seen is that of the Australian sea snail Syrinx aruanus (which gets up to 91 cm long). The two largest shells of that species I have seen are at the Delaware Museum and the Philadelphia Academy, both of which were shorter than 91 cm; I didn’t measure them, but my memory suggests they were probably 65 to 75 cm long, which is pretty big for a snail! Given that slugs are also snails (gastropods), there are reports of slug-like sea hares (family Aplysiidae) whose bodies can get nearly a meter long, but the longest one I ever saw was around 25 cm long, so the Syrinx still wins for what I have seen. Another way to answer your question about largest is not longest but instead greatest volume. For that, the sea snail Melo melo might have the greatest volume (although it’s possible a large Syrinx might also win at volume, I’m not sure).
Then again, given that my specialty is land snails, you might be asking about the largest land snail I have seen. That would be the giant African snails in the family Achatinidae. I have seen plenty of living Achatina fulica, with shells up to about 12 cm, but I have seen shells of larger species, such as Achatina achatina and Archachatina marginata. Note that we do have some large snails native to South America in the family Strophocheilidae (including a very large extinct one), but the giant African snails are larger.
Or maybe today is opposite day and you are really asking about the smallest snail I have seen. Although I do know about a minute sea snail, Ammonicera minortalia, at 0.4 mm diameter reported to be the smallest snail in the United States (Bieler & Mikkelsen 1998), I have never seen one. If you mean land snails, I recall that Wenz (1938-1944) reported some land snails in the family Diplommatinidae to be 0.5 mm, although I have not seen any Diplommatinidae that small, and I wonder if Wenz was reporting shell diameter rather than maximum dimension (most Diplommatinidae are taller than wide). (On the subject of narrow snails, I have seen the minute Carychium nannodes, which is only 0.4 mm diameter, but it is about 1.4 mm tall.) I do know some tiny snails from east Asia got a lot of press a few years ago for being able to fit into the eye of a needle (Páll-Gergely et al. 2015), and at 0.8 mm in greatest dimension, they are certainly minute, but again, I have never seen one.
The smallest adult land snails I have seen are either Punctum minutissimum or Guppya sterkii, both on the order of 1 mm diameter. Of course, their babies are even smaller, and I have seen babies of both those species, especially of P. minutissimum. Amazingly, Punctum minutissimum appears to be one of the most abundant land snails in northeastern North America, but it is rarely noticed due to its minute size.
Punctum minutissimum. Shell 1 mm (1/25 inch) diameter.
To recap (and more directly answer your question), the largest snail shell I have seen is Syrinx aruanus, the largest land snail shell I have seen is one of the giant African land snails, the largest living land snail I have seen is Achatina fulica, and the smallest land snail I have seen is babies of Punctum minutissimum.
Timothy A. Pearce, PhD, is the head of the mollusks section at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.
Bieler, R. & Mikkelsen, P.M. 1998. Ammonicera in Florida: notes on the smallest living gastropod in the United States and comments on other species of Omalogyridae (Heterobranchia). The Nautilus 111(1): 1-12.
Houbrick, R.S. 1984. The giant creeper, Campanile symbolicum Iredale, an Australian relic marine snail. In: Eldredge N. & Stanley S.M. (eds.), Living Fossils. Casebooks in Earth Sciences. Springer-Verlag, New York.
Páll-Gergely, B., Hunyadi, A., Jochum, A. & Asami, T. 2015. Seven new hypselostomatid species from China, including some of the world’s smallest land snails (Gastropoda, Pulmonata, Orthurethra). ZooKeys 523: 31–62. doi: 10.3897/zookeys.523.6114.
Wenz, W. 1938-1944, Gastropoda, Teil 1, Allgemeiner Teil und Prosobranchia. In: Schindewolf, Handbuch der Palaozoologie, v. 6. Borntraeger, Berlin. vii + 1639 p.