Unusually Large Single-Cell Organisms


Gone But Not Forgotten
Aug 1, 2005
Writeup: http://www.cosmosmagazine.com/news/...olling-seafloor

Journal article: http://dx.doi.org/10.1016/j.cub.2008.10.028

Rapidshare of Article: http://rapidshare.com/files/1685996...Traces.pdf.html

SYDNEY: Using a research submarine, marine biologists in the Bahamas have discovered large numbers of an unknown, grape-sized, single-celled animal slowly rolling across the sea floor.

"[It's] huge for a single cell. If I had cells that big I'd be six kilometres tall and weigh three trillion kilograms," said Sönke Johnsen, a biologist at Duke University in North Carolina, and the expedition's chief scientist.

Single-celled animals, known as protists, are usually the size of a pin-head or much smaller, but the size of this "sea-grape" isn't the most unusual thing about it.

"We watched the video over and over," said Johnsen. "We argued about it forever… [we thought] these things can't possibly be moving. There are other large protists, but none of them move."

Evolutionary debate

But these large protists do move, and more importantly, the tracks they leave behind are very similar to fossil tracks that date back to before the Cambrian Explosion, around 530 million years ago, when many different types of complex animal first appeared.

Because simple, single-celled animals were previously thought to be incapable of leaving tracks, the established theory is that these grooves and furrows were left by complex multi-cellular animals, and the date back to 1.8 billion years ago.

"We're confident that drawing attention to these bizarre mega-protists will provide a powerful new spin to the debate," said Mikhail Matz a biologist at the University of Texas in Austin and lead author of a study detailing the find in the journal Current Biology.

With DNA testing, the sea grape has been cautiously identified as a close relative of another giant amoeba, Gromia sphaerica from the Arabian Sea – though that species is not known to be mobile.

Slow roll

The tracks left by them, as they feed on sediment in the Bahamas, are up to 50 cm long, and it's estimated that they roll at a rate of just 2.5 cm a day. See a video slide show of the animals here.

The researchers said that it's possible that the sea grape may be a descendent of the creature that made the tracks that are well known from the fossil record. Or – like the tuatara or the coelacanth – the protist could be a living fossil, that has changed little for as many as 1.8 billion years.

"This description of similar [sea floor tracks] made by the giant single-celled amoeba is very important," commented Jim Gehling, a palaeontologist at the South Australian Museum in Adelaide. "It shows that we can never rely on one piece of evidence to demonstrate the origins of motile animals."

So I wonder what this thing looks like when it divides. It would have to be cool to watch it happen, live, without the aid of a microscope.

EDIT: Image links fixed by WJ.


Gone But Not Forgotten
Aug 1, 2005
Damn, my pictures are gone. Here's some fresh ones.

Still, I would have thought that this sort of topic would have drawn more attention. The existence of a single-celled organism that huge is the most incredible thing in this entire forum page.

And thats something.

EDIT: Hotlinked image changed by WJ.


Gone But Not Forgotten
Feb 8, 2002
Is it one of those ones that can exist as a plant as well?


Feb 5, 2011
"Scientists at the Scripps Institution of Oceanography have found giant amoebas 6.6 miles below the surface of the ocean, in the Mariana Trench to be exact. To put that in perspective: These amoebas, also known as xenophyophores, are living in a trench about 1 mile deeper than Mt. Everest is tall.

The previous depth record for xenophyophores was about 4.7 miles.

And when we say giant amoebas, we mean giant. Xenophyophores often exceed 10 centimeters (about 4 inches) across, according to a news release from Scripps, meaning the single-celled organism can be as large as a human hand. "



I knew the job was dangerous when I took it ...
Staff member
Jul 19, 2004
Out of Bounds
This round blob is a single-celled organism ...


This Eyeball-Looking Thing Is One of The Biggest Single-Celled Organisms

Throughout the world's oceans, hidden in coral rubble, you can find strange blobs of various sizes. Named sailor's eyeballs (Valonia ventricose) these squishy balls are actually an incredibly cool type of algae – they're one of the largest unicellular organisms in the world.

Indeed, that whole ball is a single cell. Now, that's not the size we'd usually associate with unicellular organisms, but sailor's eyeballs have some neat tricks up their sleeve to help them grow that big.

... They can range in size from as small as a ball bearing, all the way up to their namesake, the eyeball. ...

High-school biology classes may have informed you that cells simply can't grow that big, as there's diffusion to worry about - making something too large will mess up the surface-area-to-volume ratio.

But, although sailor's eyeballs are one cell, they contain several cytoplasmic domains, each with their own nucleus and chloroplasts. ...

This peculiar structure means that if you tried to pop it, it wouldn't just go bust like a balloon full of organelles. In fact, squashing one sailor's eyeball can cause more of them to spring up, since the organisms only need to possess one nucleus to grow into an entirely new eyeball.
FULL STORY: https://www.sciencealert.com/this-b...e-celled-organisms?perpetual=yes&limitstart=1


Dec 5, 2003
Large single cells are not rare.

You probably have a box of them in the fridge...

Eggs are single cells.

So the largest single cell would be an Aepeyornis egg.


And I like to roam the land
May 18, 2002
There seems to be some debate about whether eggs are a single cells or not. People at least seem to agree that the yolk is a cell, ie the ovum. Unless the ovum is small and surrounded by nutritious material in the form of the yolk! Others wonder if the egg shell counts as a cell wall. It seems that the definition of 'cell' is not exactly cut and dried, which is interesting.


Go away, leave me alone, nemo is home
May 10, 2006
Record bacterium discovered as long as human eyelash.

You're supposed to need a microscope to see bacteria, right? Not Thiomargarita magnifica.

This giant cell is clearly visible to the naked eye, having the size and shape of a human eyelash.
Now classified as the world's biggest bacterium, T. magnifica was discovered living on sunken, decaying mangrove tree leaves in the French Caribbean.
Fear not, the organism isn't dangerous and can't cause disease in humans. But do marvel at its proportions.
"These bacteria are about 5,000 times larger than most bacteria. And to put things into perspective, it is the equivalent for us humans to encounter another human who would be as tall as Mount Everest," said Jean-Marie Volland from the Joint Genome Institute at the Lawrence Berkeley National Laboratory, in the US.

Centimetre-long T. magnifica is not the largest single-celled organism on Earth. That's probably a type of aquatic alga called Caulerpa taxifolia which is 10 times longer still. But the bacterium is definitely impressive when you consider there are many, much more complex life forms on Earth that require some sort of magnification to be observed. Think of those really teeny worms and flies out there.
T. magnifica was first identified back in 2009 in Guadeloupe, in the Lesser Antilles. But it was initially put to one side. Only recently have Dr Volland and colleagues got around to studying it in detail.
One key finding from their investigations concerns the way the cell organises its interior. Bacteria would normally have their DNA floating freely in the liquid, or cytoplasm, that fills their bodies.
T. magnifica, on the other hand, stores its genetic material in compartments the researchers are calling pepins, from the French for fruit seeds.
It's a significant revelation because until now, the packing of DNA inside a membrane-bound compartment was considered the preserve of so-called eukaryotic cells, which are the building blocks of higher organisms such as humans, other animals and plants.
(C) BBC. '22.