This is getting spooky.It was bad enough to learn that jellyfish and the rest of the Cnidaria phylum have vision -- simple light detection in the case of the humble hydra, up to sophisticated camera-like eyes for box jellyfish.
[Valiantly resists the temptation to rant about the difference between c-opsin and r-opsin photopigments. Phyla that use c-opsins for vision, like chordates, concentrate them in cells with attachments that are specialised cilia, like human rod and cone cells. The r-opsins used by arthropods turn up in differently-designed 'rhabdomeric cells'. Each kind has its own chemical cascade to amplify the energy of an intercepted photon into a signal large enough to communicate to other cells].
Then I learned through my big sister's blog about Buddenbrockia plumatellae, a kind of cnidarian that's evolved to look like a microscopic marine worm. Imagine a jellyfish that shrank, and elongated, and became a parasite. These Cnidaria are more versatile than I had credited! Go here to read about the flabbergastingly bizarre life-cycle of Buddenbrockia, which involves proliferating in the host's tissues in the form of single cells, which then migrate into a single section of the host in the manner of slime moulds to aggregate and specialise into the worm form... possibly using the host's attempts to eal off the infection as the force that molds the worm into shape. Buddenbrockia is of course named after the family of respectable Hanseatic merchants in Thomas Mann's novel Buddenbrooks. Later generations fall out of step with shifting social mores and economic forces, lose their wealth and standing in society, and eventually become worm-like parasites that infest species of bryozoa.
Finally I discover a variety of jellyfish that has developed tentacles to look exactly like a human peripheral nervous system. Now really, people, what adaptive value can that possibly serve? If only it had evolved a facsimile of a brain as part of the resemblance, it would be able to decoy aquatic zombies into its tentacles and devour them, but that vital component of the lure is missing. Evolution has not quite completed the job.Explain that, Richard Dawkins! Adaptionist Paradigm: 0; Unintelligent Design: 1!
I can only speculate that it hopes to team up in a symbiotic relationship with the multiple-eyed box jellyfish. Those aquatic zombies will have to lift their game then.
10 comments:
A bilaterally-symmetrical Cnidarian? My world-view is shattered (I'd 'head for the hills', but they're orb-infested).
Do you recommend any literature concerning the evolutionary "history" of the diversion between organisms featuring c-opsin and r-opsin photoreceptors? Where on the cladogram would one put the split?
If only it had evolved a facsimile of a brain as part of the resemblance, it would be able to decoy aquatic zombies into its tentacles and devour them, but that vital component of the lure is missing. Evolution has not quite completed the job.
It's working on it! Rome wasn't built in a day, ya know.
P.S. :) at the helping ZRM tag.
~
Clearly that jellyfish has evolved to take over our central nervous systems. The brain slug invasion has begun!
I'm thinking that the human-nervous-system-analog jellyfish really needs to develop a symbiotic relationship with another jellyfish that can flatten itself out until it is thin and flexible enough to overlay the nervous system jellyfish with a human-skin-analog jellyfish. Then you could have them, working together, in the shape of a HUGE human, striding all Heinlein-like across the ocean floor, striking fear into the hearts of plankton everywhere...
A bilaterally-symmetrical Cnidarian?
Tetralateral, if that's any consolation.
Where on the cladogram would one put the split?
It goes back a long, long way. The earliest bilateria had already acquired the genes for *both kinds*. Some molluscs use r-opsin and have rhabdomeric photodetector cells in their eyes; some use c-opsin and ciliary photodetectors. There's a polychaete worm that uses both. Vertebrate vision follows the c-opsin strategy, but we also have melanopsin in our eyes, which belongs to the r-opsin family (it turns up in a sparse network of ganglion cells in the retina, and it seems to control the pupil response rather than have any image-forming function). Pinopsin -- the pigment that tuataras use in their 'third eye' -- is another c-opsin.
And now I see that as well as the r- and c-opsins, there's a third family of G[0]-coupled opsins, found across the Bilateria.
Cnidarian vision (or photosensitivity) uses a c-opsin like us, and some have an equivalent of the G[0] kind, so those at least had been acquired before the split between cnidaria and bilateria.
This 2006 paper from Science is good.
Here's a more recent article from the Royal Soc. -- part of a special issue of Phil. Trans., all open access.
That nervous system jellyfish, could one of them have a university job? because there's some people around here who are all nerve endings.
Thank you kindly, good Doktor!
I can only speculate that it hopes to team up in a symbiotic relationship with the multiple-eyed box jellyfish.
Marvel Two-in-One, issue #7. They perform well vs. MODOK.
some people around here who are all nerve endings.
And no branes.
a special issue of Phil. Trans., all open access.
Oops, some papers are open access and some not.
Copsin and Ropsin - didn't Beatrix Potter invent them?
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