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Valonia ventricosa (wikipedia.org)
132 points by Szpadel on July 25, 2019 | hide | past | favorite | 39 comments



I think it's a bit of a cheat to call these things single-celled. They're really lots of cells where the cells are connected by cytoplasmic bridges.

https://biology.stackexchange.com/a/28480/3871

Sure, topologically that's the same, but biology isn't topology. There are lots of organisms like this:

https://en.wikipedia.org/wiki/Coenocyte

I don't know this species specifically, but functionally, organisms like this work much the same as multicellular organisms, with the domain round a nucleus equipped with protein synthesis machinery and other organelles running mostly independently, and coordinating with the other ones via chemical signals. It's just that the signals can move around without having to cross a cell membrane.

EDIT: And if you count this as a single cell, then presumably you'll count a muscle fibre, which is also many nuclei inside a single cell membrane, in which case there are larger single cells inside your own body:

https://www.jneurosci.org/content/25/37/8528

Well, longer at least.


There's a biological and topological difference between a multinucleate cell (coenocyte) and an organism made up of distinct cells.

> if you count this as a single cell, then presumably you'll count a muscle fibre, which is also many nuclei inside a single cell membrane, in which case there are larger single cells inside your own body:

Certainly. Human muscle fibres and nerve axons are single-celled, but they aren't organisms.


Note that this is just one of the largest, not the actual largest. The actual known largest appears to be this: https://en.wikipedia.org/wiki/Syringammina_fragilissima


"It is not known how the organism feeds or reproduces"

This is amazing for me. Sometimes it seems that everything is already discovered and if not we just need to put some tech into it to analyze the mystery and get an answer.

The reality is that we are still far away from that. And that any discovery involves dedication, investment and serendipity.


Smart extraterrestrials know not to interact on land and with humans

Just like most of us dont interact with sharks and tigers


Dolphins can be quite friendly.


A decent pop-science video about them on Youtube https://www.youtube.com/watch?v=szIcnSIlrDE


Ok, we took largestness out of the title.

Or should we just change the URL to the larger one?


IMO changing the URL to point to something completely different is bad because it makes the discussion confusing.

Example: the recent discussion of a very long Cocoa identifier for a Chinese kinship term (I don’t remember the exact one) was changed to a slightly different one that was two characters longer. Making a bunch of the existing discussion confusing was not worth the value of changing the URL, in that case.


Right now, 20% of HN's first-page articles are greyed out. Before today, I don't recall ever seeing more than one or two. Does this reflect a code change?


No. What you're describing sounds like the 'visited' style for links in titles. Is it possible that you've just clicked on more stories today?


Oh. OK, I am using a different VM. With Firefox and no add-ons. So I guess that something was blocking 'visited' style.

Edit: Not NoScript.


Needs to be fixed in the title


Reminds me of slime molds. They are large single cell organisms that have multiple nuclei. A "supercell". I always wanted to keep one as a pet, but I can never find one despite them being fairly common.

https://en.wikipedia.org/wiki/Slime_mold


Very cool! As a kid I found these on the beach on vacation in St. Croix. Never knew what species they were - they turned clear after a night in a glass of seawater so I couldn't keep them.


I love seeing submissions like this on the front page. I come for the post-mortems of severe outages and I stay for the discussion of algae.


I'm amazed to see it. Valonia is a pest in reef aquariums. I can't think of anything less popular, and now it's front-page news.


Valonia ventricosa bubbles are relatively small, around 4cm. Smaller than many chicken eggs. Largest viable single cell organism is still the ostrich in its egg phase.

Unicellular organisms have zero or one nucleus. If they have two or more nucleus is multicellular


>> Unicellular organisms have zero or one nucleus. If they have two or more nucleus is multicellular

Hmm, is that true? Looks like there are unicellular organisms with multiple nuclei:

https://en.wikipedia.org/wiki/Multinucleate


multiple nuclei means division by mitosis, if a single cell suffer mitosis and split the nucleus is not a single cell anymore. Are two cells sharing the same citoplasm and membrane for a while. Cells remaining citoplasmatically connected with is brothers by a bridge by its entire life aren't uncommon in some multicellular organisms (is typical of all the kingdom fungi so is pretty common among life beings in fact).

Valonia vesicles are able to hold several smaller bubbles attached. They differenciate from the larger bubble by a process similar to gemation and quickly replace it when is too old or damaged and it bursts. If a bubble equals a cell in function and looks, an organism able to have rhizoids and other smaller cells glued to its main cell, is clearly pluricellular.


For those interested in organisms without a nucleus they're called prokaryotes [1], and apparently red blood cells don't have nuclei either.

[1] https://en.m.wikipedia.org/wiki/Prokaryote


What would this taste like?


Assuming you pulled it straight from the sea, it'd probably be salty and slimy.

The internals of cells are mostly water, protein, and DNA, which don't really taste like anything to our tongues. Most sugars are stored as glycogen, so you wouldn't get much sweetness. There also wouldn't be much texture, as it's lacking any sort of bone or shell.


You are describing an extremely nutrient-rich food with no immediately apparent defence against predation. To the extent that it is difficult to understand how this could exist in the wild.

I suspect that this alga has some interesting and perhaps surprising defences, in line with its relatives. (And, that these may well impact on its taste)

For example, spirulina is said to be spiral because this allows it to spontaneously flee from approaching water fleas, with no active energy use: primarily depending on the laws of physics.


If we leave glycogen in our mouth for seconds/minutes, would the acids in our mouth decompose it into glucose which would taste sweet? Yes, I have no knowledge about chemistry.


Nope. There is no acid in the mouth, and acid doesn't break down carbohydrates anyways, its all enzymes in the intestine.

Amylase, the thing in the mouth, breaks down starches, like in rice or bread. Glycogen is different from these though, as it has different linkages, and can't be broken down by amylase.


Thank you!


Like a mouthful of saltwater in a sour envelope packed with razor blade-like microcrystals of silica and calcium carbonate.

Probably edible in a strict sense (if growing in clean waters), as Codium and other similar algae are, but the experience wouldn't be pleasant.


with a diameter that ranges typically from 1 to 4 centimetres (0.4 to 1.6 in) although it may achieve a diameter of up to 5.1 centimetres (2.0 in) in rarer cases.

Mind: Blown


What about dinosaur eggs?


> An organism refers to any individual living thing that can react to stimuli, reproduce, grow, and maintain homeostasis. It can be a virus, bacterium, protist, fungus, plant or an animal.


This creatures defy definition boundaries. Some act as animals with structures to run and travel fast, but can photosinthesize also so can fit at the same time in the old definition of plants. Currently they are neither animals nor plants. Some fungus walk and climb and some bacterias can act "like a beehive" with a collective purpose in some phases of its cycle. Bacterias reproduce when divide, but often its cells remain losely attached in tetrads or chains.

Bird eggs increase its cells by division and sometimes a single egg can produce two twin animals. Are they reproducting?. Well, in some sense, yes.


Or ostrich eggs, for that matter....


What does this look in the inside?


Apparently it consists of a very large vacuole, surrounded by a thin layer of cytoplasm. Has multiple nuclei and chloroplasts spread around.


Are any of the organelles visible to the naked eye?


The cell is a little scaled-up, but the organelles are of normal size.


Heh. So it's like a regular cell but everything inside of it is full of padding? What is it padded of, water?


No padding, just lots and lots of organelles.




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