Ctenophores: Wonders of Biology
quantamagazine.org
quantamagazine.org
Amazing to learn they were cilia refracting the light, not chemical bioluminescence, and that despite appearances they are absolutely not jellyfish!
And they are nor just bioluminiscent, they are strongly bioluminiscent. Cilia adds motion to the spectacle and maybe can change its color, but they definitely can turn on and off the lights. The cilia pads are used mostly for movement.
Many of this animals live in places without much light and do a vertical migration at night, each night. All are carnivores of small preys and is assumed also that they use light to lure its preys near their sticky longlines. Very abundant and probably one of the zoological groups were we could still find suddenly thousands of news species, but studying them is a nightmare. They literally melt when manipulated or in the microscope. At the sea, if they are cut the biggest chunks can regrow a whole body.
Its chemical lights can be used by us to detect toxics in the water. They react to contaminants making the luminiscence much brighter. Just as if they were alarmed and trying to warn other.
I wonder just now, if there is a hidden language there, like with bees dancing to communicate with other bees. Who knows. The problem is that they don't have eyes (If I remember correctly) so would need some other mechanism to see the lights. Maybe chemical.
Is a good example of how trying to equal how other animals experience the world with our experience is a mistake. Imagine seeing light with your tongue. This animals could even not be aware that they are bioluminiscent.
It seems that emitting light when eaten is a final defense to attract the attention of your consumer's predators to protect others members of your species from a similar fate.
It's real, and that's a real video, but it's a very weird, very atypical ctenophore.
https://en.wikipedia.org/wiki/Venus_girdle
The "Venus's girdle" is a long thin flat belt-shaped thing, but it is not wormlike. It has no head, no sense organs or anything, and the "mouth" and other main organs are in the centre of the belt, not at one end like a worm or a snake -- or you.
Most ctenophores are called "comb jellies"; one group is named "sea grapes". They are hard to generalise and not all are like this by any means, but most tend to be small, and egg-shaped, possibly with protrusions. Most tend to have 2 long trailing tentacles they use to catch food.
Most don't have muscles. They swim using bands of cilia,which are the same fine hairs that unicellular organisms use to swim, and that line your bronchi and throat. Your body uses cilia to propel mucus out of your lungs and up to where you can cough it up.
Comb jellies' cilia are in long lines, usually 8 rows. They move like a Mexican wave in a sports crowd. The light refracting through these near-microscopic beating hairs looks like they flicker with rainbows. Thus the name, comb jellies. They are often radially symmetrical along the line from mouth to other end.
That's all they have; no legs, no fins, no eyes, no dedicated sense organs. Most are not bioluminescent, but like I said, there's pretty much nothing you can say about comb jellies that applies to all of them. One type is an internal parasite that looks like a worm, although internally it's nothing like a worm. (That one is not 2-way symmetrical like us and most animals; it's four way symmetrical. It is alien compared to all other wormlike things.) Other parasitic ones are just small branching bags that don't move.
They are about the only multicellular animal that swims with cilia. They are so unlike all other multicellular animals it's just about possible that they evolved the whole plan of being multicellular entirely independently.
They look like jellyfish but are nothing like them.
Jellyfish have lots of tentacles; those comb jellies that have them, have 2, no more, no less. The tentacles don't sting; they are sticky, and the animal catches tiny plankton this way and pulls them up to its mouth to eat.
One type, Beroids, have a mouth they can close, and they can actually swallow other smaller jellies (comb jellies or jellyfish). Their lips zip shut from the edges and they have more cilia inside to propel the prey down their "throat," but they can't chew.
Some have muscles and can flex and move. Some but not many sort of swim this way, like the Venus's girdle. A very few stick to the bottom and stay there.
Comb jellies tend to have a front end and a back end, but most have no anus, just 1 hole; any food waste is vomited. But, rather wonderfully, some form an anus only when they need to poop and then it closes up again, "heals" shut, totally gone.
https://www.livescience.com/64956-ctenophore-sometime-anus.h...
They are just wonderfully weird.
They are not really alien; their genetic code is the same as ours, although they don't do things all other animals do. For example their nerves do not have synapses, so they don't need neurotransmitters to carry signals across the joins between nerves. They don't have joins. Their nerves are a continuous mesh, with long lines of cytoplasm dotted with nuclei, not divided up into separate cells -- the same sort of structure as most fungi, but flexible.
I think they are beautiful. Little was known about them when I did my biology degree, but I got into them about 5 years ago and read a lot about them for a while. They are like nothing else. Even the parasitic ones, while kind of nasty, are deeply weird.
Phyla?
So I can’t vouch for that first video, but I can vouch for the rippling rainbow cilia (scroll down to the second video on that page), they really do look like that IRL.
They’re very pretty.
I've long wondered: What is the difference between cilia and flagella? I've found no authoritative source that differentiates them or that says they are the same (except one paper from decades ago that strongly implies they are the same). It seems like something insiders know implicitly and never bother explaining.
Because a clear distinction is lacking, I don't trust non-expert sources like Wikipedia to be consistent, tor to not confuse them or miss any nuance.
There are clear structural differences at microscopic level. they are fueled differently. In short, cilia are like eyebrow hairs, short, weak and simple. They appear in groups of tens or thousands, while flagella are like head hairs, unique or double, rarely more than three, and much longer, thicker and more potent, so faster. Structurally more complex also.
They move in a different way also. Lets say that cilia move like a pendulum and flagella moves like the ribbons in rhythmic Gymnastics
Broadly and generally:
• cilia come in large groups, in rows or in sheets; flagella come singly or in pairs (occasionally more)
• cilia are short, and they beat backwards and forwards in a coordinated way, like a Mexican wave; flagellae are long, and in prokaryotes, they spin around their axis.
(Eukaryote flagella -- e.g. spermatozoan "tails" -- are a different structure that just resembles the ones in prokaryotes. Prokaryotes are bacteria and archaea -- no cell nucleus. Eukaryotas have cell nuclei and other organelles, such as mitochondria and chloroplasts. Their flagellae bend and flap, they don't spin.)
Take 1 cell. Can you count the moving hair things? Then they're flagella. Is the beastie covered in lots of them, countless, like fur? Then they're cilia.
> in prokaryotes, they spin around their axis.
I read earlier this year about Berg's and Samuel et al.'s (and maybe others') amazing flagellar motor discoveries. I didn't realize they were only prokaryotes; the motor seems like a sophisticated mechanism.
However, we have ATP Synthase. That’s also an ion driven molecular rotary engine. Of course, we use it to convert ionic gradients to energy (ATP).
Both are exceptionally efficient molecules for their tasks.
But the thing is that, AIUI, ATP-synthase is in the mitochondria and chloroplasts, so from an evolutionary perspective it is in prokaryotes... just symbiotic ones...
In some ways, it’s wrong to imagine the branches of life are actually branches. Loki archea and alphaproteobacter together gave us the last eukaryotic common ancestor, and then bacteria continued to live around and in eukaryotes.
That said, mitochondria can’t be called prokaryotes within us. They’ve given up too many genes, and can’t survive on their own.
Of course, the rest of us can’t survive without them either, so it’s a complete mutual situation.
I'm not sure that adds up: It's not that much longer - 500 million years out of ~3.5 billion?
And the evidence shows that Eukaryotes have evolved much faster and further - just look at the Eukaryota domain. And IIRC part of the reason is advantages such as 'sexual' [0] reproduction - rather than just splitting and (cloning?) DNA, combining chromosomes from two parents.
[0] If that's the correct term.
But the first complex multicellular life only appears about 1.6 BYA, and sexual reproduction and cell differentiation only about 1.2 BYA.
And no, I wouldn’t say eukaryotes have evolved faster or further, just differently. It’s questionable they’d be able to do any of this without the mitochondrial and chloroplast endosymbiotic events, and microbiomes have existed since the beginning as well. Framing it as a contest misses the point, in the end.
Interesting case of nominative determinism.
But yes, the I suppose a call to study ocean creatures can be more compelling with that’s name.