This exceedingly strange sea creature is of the kind one might expect to discover among the pages of one of Hugh Lofting's Dr Dolittle books. It seems to have been seen only once and that was in the 16th Century in the Baltic Sea. For those not well-up in geography, that's the one that stretches from Russia to Denmark.
However, I doubt that this creature was really a snail, however much it may have resembled one. Its eyes were on either side of its head and it had small paws. Now, a snail is a gastropod, which means its foot and stomach are one or, if you prefer, its stomach is used as a foot. Self-respecting snails do not have paws. Nonetheless, we don't know just what it was. I know of no further sightings so, just in case you are a French restauranteur thinking "Here would be a magnificent source of escargot," don't get your hopes up.