Unusually Large Single-Cell Organisms

Iggore

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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.
 

Iggore

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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.
 

Vardoger

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I've seen a photo of single cell organisms being tested in mazes. They actually learned how to navigate the easiest way out. So they got to a have neuron in their body, or rather the whole body is a neuron. Amazing "creatures".

http://news.bbc.co.uk/2/hi/science/nature/944790.stm
 

river_styx

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Is it one of those ones that can exist as a plant as well?
 

kamalktk

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"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. "

http://latimesblogs.latimes.com/nat...eba-found-mariana-trench-beneath-the-sea.html
 

EnolaGaia

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This round blob is a single-celled organism ...

sailor-eye-ball.jpg

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
 

Kondoru

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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.
 

James_H

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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.
 
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