At first, the whole sea was sea. This was the case for a billion years until small structures began to be ordered forming tiny “capsules,” separating the outside world from the inside. They were phospholipids, molecules whose ends have opposite tastes. While one side is attracted to water, the other repudiates it, it is hydrophobic, just like a drop of oil.
Over time these molecules were grouped and ordered, like the tiles of a mosaic. Next to each other, lining their hydrophilic parts towards the rough sea and gluing their hydrophobic parts with each other, doing as a double membrane that would protect them from water. Soon, the layer curved, closing in a sphere of phospholipids, a partition between the vastness of the ocean and what would end up being the first cell.
Many more steps were necessary so that this “micelle” could be called a cell. He needed organelles capable of carrying out basic functions, but he had made a decisive breakthrough, the cell was defined, existed and could be regulated regardless of what happened outside. Thus, the cells developed, evolved and grew, although not without limits, because if we imagine a cell as a sphere, we will see that not everything goes.
Size does matter
For small cells, the surface of the sphere is enough to exchange everything you need to survive with the outside. However, as its size increases, its interior grows much faster than its surface and the membrane becomes too small to “feed” a similar monster. They are things of geometry, the volume of a sphere grows faster because its formula multiplies 4/3 by “pi” and its radius to the cube, Meanwhile, its surface responds to four times “pi” by the radius squared. As the volume formula multiplies the radius by itself three times, compared to the two that the surface does, any change in the radius of the sphere is much more noticeable in its volume than in the surface; the inside grows faster than the outside.
That is why, for a very long time, it was thought that it was impossible to find a giant cell. However, we were wrong. There is a group of living beings, the xenophiophors, which are formed by a single cell more than 10 centimeters in diameter. They are really huge to be a cell, but we can appreciate them better if we compare them with the largest cells in our body, the ovules, which measure 0.14 millimeters, 1,500 times less than a xenophiophore. A difference that becomes even greater if we put it next to other cells with a more standard size, such as red blood cells, just 0.006 millimeters in diameter. Xenophiophors are true colossi of the cellular world, they challenge what we thought we knew about cell size. But then how do they survive their huge size?
Like sea croquettes
What is the trick of xenophiophors? How can they not starve to death with their ridiculous spherical surface? Ah! That is exactly the key. We have thought about round cells or at most rounded, but what happens if we let the imagination fly? Not all geometric objects have the same relationship between their surface and volume, the more elongated they are, the more the ratio between the two measures is equalized. Something like this happened with the xenophiophors, as they grew up, they formed a partitioned structure, full of branches that were divided and reunified as a large network in three dimensions, coming to take forms of fantasy.
And this is not all, because just as a country that is too large cannot be governed from a single point, the xenophiophors multiplied its nucleus. A structure that we could compare with the “director” of the cell and where the genetic information is hidden, the DNA. These were two tremendously ingenious solutions to complex problems. However, the fragility of the phospholipid membrane was a setback that the xenophiophors “solved” in a much less … elegant way.
As a solution, its surface produces a mucous substance to which pebbles, sand and other debris from the seabed adhere. Thus they form a scab called “testa” that, like the breaded croquette, protects it from breaking into a thousand pieces. In fact, the same name “Xenophyophora” means in Greek “carrier of foreign bodies.”
Triton in the Faroë Islands
The xenofióforos were developing all these adaptations over millions of years, little by little, allowing them to grow without limits. They lived calmly at the bottom of the ocean, until John Murray docked his ship Triton in the Faroe Islands, back in 1882. The rough sea of the Scottish coast was a place as good as any other for the oceanographer. What I didn’t expect was to find Titans under their waves. That surpassed Murray’s taxonomic knowledge, so he decided to take samples of the xenophiophore and send it to his colleague, naturalist Henry Baker.
The material was so delicate that, when he arrived at Baker, it had completely torn apart. They were like fragile sand tubes, and in fact that is what the name they gave the species means “Syringammina fragilissima”And Baker tells it like this:
The first xenophyophoro had been discovered, and although it has taken many attempts to classify it, it seems that they belong to the kingdom of the proctists, such as amoebas or algae. One of the paradigms of cell biology had changed forever. Those cells were larger than previously thought possible, in fact, although they usually measure 10 centimeters, this particular species can reach 20.
Since then we have not stopped discovering xenophiophors. At the beginning of 2020 we already have more than forty different species, spread across all the oceans of the planet, populating from 500 to 10,000 meters deep. In fact, there are so many that some of its colonies are overcrowded, reaching more than twenty individuals per square meter. But, being so many, how does that impact your environment? We now know that xenophiophors can alter the way sediments that form the seabed are deposited, modeling their own world of sand.
Moreover, recent studies seem to point to the fact that bioturbation produced by stirring the seabed could be beneficial for other species. Something that is suspected of having found concentrations of xenophiophors surrounded by more than 3 times the amount of crustaceans, echinoderms and mollusks that we could see in other areas. Even their testa is useful for the ecosystem, as it seems that, during periods of growth, they detach from some of its fragments, which other organisms can colonize.
As for his habits, however, we continue to ignore almost everything. They feed mainly on debris that surrounds with bumps called “pseudopods.” Accumulating high concentrations of barium sulfate, lead, aluminum and even uranium in your body without seeming to affect them too much. One of the few clues we have about your diet are the large amounts of lipids of apparent bacterial origin that are stored inside. This suggests that bacteria are their main course, although the surprise may be in how they hunt them. The xenophiophors could find these bacteria among the sediments, or what is even more interesting: to raise them in their testa, feeding them with the waste that their mucus was adhering.
Sometimes, when we are told about the mysteries of the great blue, they show us whales and tropical fish, majestic animals that are visible, but there are some exciting stories of beings that, if you do not know, their appearance can make them pass unnoticed Breaded in sand and food debris, xenophiophors have kept their unicellular nature a secret for centuries. However, we already know part of what is behind his head, we understand the challenges they have had to face in order to survive as a single colossal cell, in the middle of a world made on another scale.
Only that already generates surprise, but it is still a tiny part of what we can discover in the future. They are absolutely strange life forms that have found different solutions to the same problems that we all face. Survival has pushed them to be, possibly, one of the most alien life forms we have on our planet.
DON’T KEEP IT UP:
- Despite what is usually thought, eggs are not a single cell, they are formed by complex structures within which the embryo will form. The confusion comes from the English term “egg” which means both “egg” and “egg.” Thus, xenophiophors are the largest cells of which we have evidence.