It’s the end of XIX century. A man, far away from home, looks in his microscope. He’s looking at a drop of salty water, taken from a salt pan, where tiny creatures frolick. One attracts his attention. The man looks closer. It’s an unknown thing. Still staring at the eyepiece, he begins to sketch on his notebook. It is not simply a new tiny animal. It is something so simple to be inevitable.
It is the long-awaited Ur-animal, the simple ancestor of all of us. Every individual, no bigger than a quarter of a millimeter, is an elongate bag, one cell thick. Both the inner and outer surface are hairy, covered with cilia. The opening of the bag is a mouth, with somewhat longer cilia surrounding it. These funnel the food in the simplest digestive system ever: a cavity where cells absorb the food. That is it. A microscopic bag of a hundred cells, with a mouth and hair.
The creature is named Salinella salve, and it is the only known member of its group, the Monoblastozoa (“animals with one cell layer”). It looks like the crystal-clear missing link between single-celled creatures and multicellular animals. And no one has ever seen it again.
All we have of Salinella are the thirty, yellow pages that the biologist Johannes Frenzel published in 1896, in a monography on the microscopic fauna of Argentina. Nobody ever found Salinella again: not in Argentina, nor elsewhere. An expedition in 2012 attempted to go back where Frenzel supposedly found it. Instead of the salty lakes Frenzel described, they only found cows and plains. They looked for every salt pan nearby and examined their waters. Nothing resembling Salinella was ever found.
Nonetheless, biologists kept perpetuating the memory of Salinella. It is found in zoology textbooks, in encyclopedias, in recent papers about the evolution of animals. It is still there. The description by Frenzel is not a mere sketch, after all: it is a serious, detailed description of a living, breathing creature, where every piece makes sense, with detailed drawings of the organism and of its cells, with descriptions of its reproduction and motion. It looks real, and it has been considered real after.
Clever hoax, interpretation mistake, delirium of a lonely German biologist: whatever its origin, Salinella is perhaps the last mythological animal populating the biology textbooks, the last relic of an age where legend and history were inextricably tied. Like many of these creatures, it still tantalizes us because, as the nexus between before-animal and animal, it occupies a crucial place in our world of ideas. However, when with exploration our world became smaller, so the habitats of imaginary beings. Krakens infested insondable oceans, blemmyes populated the heart of unknown Africa. Their last heir instead it is said to live, tiny and untraceable, within an unknown salt pan, in Argentina.