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Allow me to parade my ignorance and ask a question to the marine biologists and microbiologists on Google+.

There have been some stories in the press over the weekend about a voyage to a deep sea trench, where biologists have found 4-inch-wide amoebae. I will be the first to declare this to be a very cool discovery. But the press release and the articles alike have referred to them as "the largest individual cells in existence."

What about ostrich eggs? What about acellular slime molds that can stretch yards across? Is this just overenthusiastic spin, or does it hinge on some fine legalistic definition of "cell"?

(I can't track down a journal paper describing the results. I've contacted Scripps to see if there is one, and to get an answer to my question. No response yet, but, hey, it's Sunday morning as of this writing.)

Update 10/24/11: I heard back from the Scripps press office, which relayed this short message from one of the scientists on the project, Lisa Levin:

"I don't have an opportunity to research cell size on the planet. Given that the other two examples are terrestrial (I think), perhaps we just leave these as the largest single cell organisms in the ocean?"

Seems right to me. Any thoughts? The press release (and articles following it) have not been changed.
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Maybe it is definition, but only the yolk of the ostrich egg is a single cell, isn't it?
 
Well, we were just talking about this issue in my intro bio class because I mentioned these organisms (before the new press). I was on a deep sea cruise in 2002 where one was brought up and I have had it in the freezer for years. I was describing this foraminiferan (they are NOT amoebas BTW) to the class and said they had these giant cells. And one of the students asked basically your question. So I have been looking into answering it. I think the definition of what a single cell is is critical because many cells cane very large but many of these have multiple nuclei and in a way are a cheat. They sort of are many cells, they just did not form a full membrane/wall to separate the different compartments.
 
Also - what about giant nerve cells in giant squid? They are used as a model because the cells are huge (longer than wide though ...)
 
Maybe it's the largest eukaryotic cell, with a cell membrane and all of the organelles, such a a nucleus, mitochondria, etc?
 
If these things count, then so do Caulerpa and those are bigger, I think (they say 'individual', so I'm not sure if that would exclude neurons and eggs). I think it's just some spin, to get people interested. For some reason, people seem to be interested in 'biggest', 'tallest', 'smallest' and those kinds of factoids.
 
I've heard nerve cells in the leg of giraffe are considered some of the largest single cells. I've heard these cells found in the deep sea sample are ~10cm in diameter. Maybe it's the diameter measurement they are using?
 
I'd put this down to enthusiasm.

But.

As +Jonathan Eisen mentions, cells with many nuclei probably can be thought of as a different category. Ostrich eggs are large mainly because they have a huge amount of stored food.

I haven't seen estimates of the total volume of giant neurons in very large animals. I doubt anyone has shown in many cases, particularly vertebrates, that they are single, continuous neurons. I could probably make some decent estimates for giant neurons in lobsters.

So these new cells may be the largest independently living cells with a single nucleus.

They're cool in any case.
 
I think when they say "individual cell", they mean "single-celled organism". An egg or a neuron is not, in itself, alive.
 
Honk if you love slime molds! I love it when I get an inflorescent of Dog Vomit slime mold in my mulch!
 
Squid giant axons are fused cells with multiple nuclei, though.

This might mean that in terms of volume, medial giant neurons in lobsters might have a case for biggest single neuron by volume. I may have to do some calculations and blog it later.
 
Until the first few divisions are complete, an unfertilized teleolecithal egg is one gigantic cell with a continuous cell membrane. For a bird egg (we're talking ostriches here for the win), I can't remember when the blastomeres cut themselves off from direct communication with the yolk. I do agree with you, though, I think they mean largest single celled adult organism.
 
Then we definitely have a case of hype, don't we?
 
From reading the press release, it seems like the press person took it out of context. Meh, what are you going to do?
 
As geologist, I might have to explain what I learned about these xenophyophores.
They are definitely not a new species, it was discovered in 1882 by Brady et al. with the Syringammina fragillissima, offshore Scotland. It's a classic example of living giant foraminifera.
There have been an interesting hypothesis that, before the Ediacaran life explosion of 650-550 MY, life was mainly consisting of giant protists similar (but not the same phylum) to xenophyophores.
I said mainly because sponges appeared a bit before the Ediacaran period, during the Cryogenian, the famous (and also over-hyped) snow-ball Earth.
 
+David Wood Eggs are a single cell, their Nucleus is the yolk of the egg.. So in diamater (XYZ size... Erm.. depth? Volume? shrug*), the eggs may be the biggest cells and the acellular slime molds, are probably the biggest cells (that i've heard of) in surface area. They may be the biggest single celled amoebas, as opposed to a mold or an egg.. *shrug
Interesting though!
 
The egg contains a single cell but the yolk is not the nucleus of this cell. The yolk of non fertilized egg is made of this cell. In a fertilized egg, the yoke is not a cell anymore nor a part of a cell.
 
I never understood how the ostrich egg was the 'biggest cell'. I have a vivid childhood memory of telling my kindergarten teacher that and having to sit in the corner for disgreeing. Just how big is the actual ova cell prior to division, anyway? Is it really as big as an ostrich egg? Doesn't make sense.
 
Prior fecundation, the egg has no shell. The yolk AND the germinal cells (1/2 chromosome set) are one single cell. The white (albumen) is outside and cannot be considered as a part of the cell, this is just a gel maintaining the germinal cell in suspension with 2 more solid 'ropes', the chalazae.
I don't know the size of the yoke of an ostrich prior fecundation, but it might be big. More than 10 cm ? I don't know.

When I was 11-12, I read a scifi book (can't remember the author nor the name) where all amobea and other protists were growing the size of a human. The earth was covered by a jelly. This is a bit what we have here undersea.
For french people, they might also remember Jelly, the giant amobea of 1000's of sqkm which has telepathic power, staying on top of the Pacific ice in the "Compagnie des Glaces" of G-J Arnaud.
Sometimes, scifi is more realistic than "reality".
 
Regarding your update: I can't agree with her, due to Caulerpa being aquatic. Maybe they can go with "the second-largest single-celled organisms in the ocean"? :-P
 
Labeling "largest" is nearly always tricky business. Of note in this particular discussion, if one is interested in length, are the axons in the vagus nerve, specifically the component forming the recurrent laryngeal nerve. This is an exceptional long nerve in modern giraffes and other animals with extended cervical regions (i.e. big necks). However, what's particular interesting is that this particular nerve is so consistent that we can also reconstruct its course with confidence in extinct taxa, which means we have a good idea of the length in things like sauropod dinosaurs, which would have been many tens of meters. This is the topic of a paper in press by Matt Wedel.

He has posted a discussion of it here: http://svpow.wordpress.com/papers-by-sv-powsketeers/wedel-2011-on-long-nerves-of-sauropods/ There is a link to a preprint copy of the paper, as well.

Further discussion also point your cursors here: http://svpow.wordpress.com/2011/05/23/the-worlds-longest-cells-speculations-on-the-nervous-systems-of-sauropods/
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