What are xenophyophores and how do they form their unique structures?

[Pythagorean]

I never knew...

Xenophyophores are essentially lumps of viscous fluid called cytoplasm containing numerous nuclei distributed evenly throughout. Everything is contained in a ramose (highly branched) system of tubes called a granellare, itself composed of an organic cement-like substance.

...

Their glue-like secretions cause silt and strings of their own fecal matter, called stercomes, to build up into masses (called stercomares) on their exteriors. In this way, the organisms form structures that project from the sea floor; this characteristic is also the source of their name, which may be translated from the Greek to mean "bearer of foreign bodies". A protective, shell-like test is thereby agglutinated around the granellare, which is composed of scavenged minerals and the microscopic skeletal remains of other organisms, such as sponges, radiolarians, and other foraminiferans.

http://en.wikipedia.org/wiki/Xenophyophore


Fascinating!

 

[Monique]

Exactly what is the evidence that it's a single cell?

 

[aroc91]

Exactly what is the evidence that it's a single cell?

Wikipedia's own source material?

Kingdom: Rhizaria
Phylum: Foraminifera

xenophyophores may be more than 20 cm in diameter-yet they are composed of only one cell

http://oceanexplorer.noaa.gov/explorations/03windows/background/education/media/03win_giants.pdf

 

[Monique]

That's a statement, no evidence How do you put a structure of 20 cm diameter under the microscope?

I think it is really interesting, I've regularly attended presentations on limits of cell/organism size, but I've never heard of this organism before.

 

[Pythagorean]

I see hundred of sources in google scholar talking about it being single-celled in their introduction without a hint of controversy, but I don't see any papers that actually show it. Maybe it's self-evident if you have one in the lab? I don't know, I guess I just took it for granted.

They refer to them as multi-nucleate. They're found in the Mariana Trench (which attracts lots of biologists because it's a unique habitat).

 

[Dickfore]

Exactly what is the evidence that it's a single cell?

What's the evidence that a chicken egg is a single cell?

 

[Monique]

How could it be self-evident? It's not that I don't believe it, it's just strange that there are no actual scientific papers on the organism. Well, I've found one very old Science paper but at a glance it doesn't really describe the cellular biology.

It needs to be multi-nucleate for it to sustain such a large cellular area, it must undergo very extensive endoreduplication. I wonder whether it can undergo mitosis and how it generates progeny..

 

[Monique]

What's the evidence that a chicken egg is a single cell?

It isn't a single cell, it's an amniotic egg.

 

[Pythagorean]

Syringammina fragilissima is the latin name for the particular species of Xenophyophores that reaches 20 cm. Maybe it will be easier to find the "first" report on them with that name.

Hrmm... they've been studied for at least 150 years. Here's 100-year-old publications that have record of it:
http://www.biodiversitylibrary.org/name/Syringammina+fragilissima

 

[Dickfore]

It isn't a single cell, it's an amniotic egg.

I think it is a single cell, but it is not a single-cellular organism yet.

 

[Pythagorean]

The biological "egg" itself is a single cell. If you include all the support/nutrtion cells in the yolk, then you could call it multiple.. I guess.. kind of... if you stretch it. But there's only one actual egg cell in the unfertilized egg.

 

[Monique]

I think it is a single cell, but it is not a single-cellular organism yet.

You are derailing the thread, you can make this a matter of definitions (what is a cell). Don't expect the entire chicken egg to undergo cytokinesis as it goes from a one-cell to a two-cell stage. http://wfscnet.tamu.edu/TCWC/Herps_online/Hibbitts/Amniote%20features.pdf

Let's get back on topic, interesting relevant paper: http://www.unige.ch/sciences/biologie/biani/msg/files/pdf/Pawlowski_JEM2003_Syringammina.pdf

 

[jim mcnamara]

FWIW - the plasmodial stage of slime molds is a single multinucleate cell. If you took mycology in the 50's and 60's, college labs often had a "pet" Physarum polycephalum in plasmodial stage. They are amazing.

And the glob of cytoplasm which is the plasmodium is large and yellow. I remember watching streaming under the microscope. I don't see a problem with other species reaching 20cm as a single cell. The fact that plasmodia are single celled was described in the 1880's, and I do not have the citation. But: See C. Alexopoulos 'Introductory Mycology' (whatever edition you can find in the University Library).

Slime molds are no longer classified as fungi, but may still appear in modern mycology texts.

 

[Monique]

FWIW - the plasmodial stage of slime molds is a single multinucleate cell. If you took mycology in the 50's and 60's, college labs often had a "pet" Physarum polycephalum in plasmodial stage. They are amazing.

What approximate size was it?

I don't see a problem with other species reaching 20cm as a single cell.

You don't? I can think of one and it's in the name of the organism: Syringammina fragilissima.

 

[jim mcnamara]

I meant I do not see a problem with the actual existence of really large cells. Sorry.
I was not speaking to anything other than the fact that there was expressed reasonable disbelief in the fact such a thing could exist.

 

[atyy]

Xenophyophores
Protozoa in the Deep Sea
"Some foraminiferans and all xenophyophores appear to be multinucleate"
http://palaios.geoscienceworld.org/content/9/1/32.full.pdf+html
"Xenophyophores are large agglutinating protozoans that live primarily in the deep sea. They form elaborate tests that range from several mm to 25 cm in the longest dimension (Tendal, 1972). Although xenophyophores are among the largest living single-cell organisms (Margulis et al., 1989), little is known about their biology. Until twenty years ago, few scientists working in the deep sea recognized them as protozoans. They were often assumed to be sponges or mud lumps, and the fragile tests were usually recovered as fragments (Tendal, 1972,1979). Collection of intact specimens has increased dramatically with improvements in the design of sediment corers and through greater use of submersibles. In a recent handbook on the Protoctista, Xenophyophora is listed as one of 45 protozoan phyla (Margulis et al., 1989). The name Xenophyophora, meaning "bearer of foreign bodies," refers to the sediments, called xenophyae, which are agglutinated to form tests. Within the Xenophyophora there are 2 classes, the Psamminida and the Stannomida, distinguished mainly by the presence of thin (3-4 ,Lm) fiber-like threads called linnellae in the latter class. "

Gromia sphaerica
http://www.bio.utexas.edu/research/matz_lab/matzlab/Papers_files/sea%20grapes%202008.pdf
http://www.bio.utexas.edu/research/matz_lab/matzlab/News/FFC399B2-91BD-4D44-85B5-C2693EB9101C.html
Big Blobs Change View of Evolution
Giant Protists on the Sea Floor
"In this video taken from a submersible in the Bahamas, a large population of giant protists (Gromia sphaerica) can be seen scattered across the ocean floor. The protists have moved up the slope and left animal-like tracks in their wake. The shrimp is about 20 cm long."

How do you put a structure of 20 cm diameter under the microscope?

Sounds like a sectioning job from hell.

THE XENOPHYOPHORES OF NEW ZEALAND (RHIZOPODEA, PROTOZOA)
by O. S. Tendal
Zoological Laboratory, University of Copenhagen
"Much of the internal structure of the xenophyophores can be investigated with a common dissecting microscope, the specimen being immersed in alcohol or water. Their cytology can be viewed in stained sections but good sections are difficult to obtain because the xenophyae are difficult to cut and tend to cause displacement of other structures."

 

[BlackTentacle]

I am gobsmacked!

 

[Pythagorean]

On the converse side, multicellular organisms can be smaller than amoebas:

http://blogs.discovermagazine.com/n...y-wasps-cope-with-being-smaller-than-amoebas/

 

[Ryan_m_b]

On the converse side, multicellular organisms can be smaller than amoebas:

http://blogs.discovermagazine.com/n...y-wasps-cope-with-being-smaller-than-amoebas/

Put's into perspective how big some amoebas can be! Over 200μm?? That's pretty much visible to the naked eye!