This Isn't Related To Cephalopods At All, But Re: Bilateral Symmetry, There's Actually Some Fairly Recent

this isn't related to cephalopods at all, but re: bilateral symmetry, there's actually some fairly recent (like, last 15 years) evidence that cnidarians actually evolved from bilaterally symmetric ancestors! Contrary to popular belief, a lot of sea anemones and coral polyps, though externally radial, actually have a bilateral digestive system. This could be a case of convergent evolution, but what's really remarkable is that embryonically, cnidarians develop this bilateral symmetry the same way as bilaterians, *using the same regulatory genetic pathways*! The polyp body plan is considered to be the ancestral state for cnidarians, while the "simplified" swimming jellyfish body plan probably is a secondary development, as suggested by the cnidarian fossil record and evidence of loss of body patterning genes in jellyfish. Together, this suggests the really exciting hypothesis that bilateral symmetry is actually the original ancestral state for the common ancestor of cnidarians and bilaterians, and rather than bilaterians being the ones who made the innovation of bilateral symmetry from radial, cnidarians would be the group that altered their symmetry instead! Sources: 1, 2, 3

(Echinoderms like starfish also are secondarily radial; they have bilateral larvae who undergo a very weird metamorphosis into their pentaradial adult form. Search "brachiolaria", "pluteus larva", or "auricularia larva" for pics!)

It's also a common misconception that cnidarians don't have central nervous systems. They're often said to have merely diffuse "nerve nets," and they do, but they also have a condensed ring-shaped nerve that integrates signals from across the body, basically constituting a central nervous system in all respects besides not actually having a singular "brain". In particular, there's been a lot of research into the nervous systems of box jellyfish, which are probably the most specialized among cnidarians due to their unique possession of true image-forming eyes, which they use for navigating both long and short distances as well detecting prey. One study from just last year even found evidence that box jellies display associative learning! Sources: 1, 2, 3, 4

(I believe there's also been research into the learning capabilities of echinoderms but I'm not as familiar with the literature. I know starfish do actually have image-forming eyes on their arms, which at least one species uses to navigate, though they also definitely do a lot of smelling and stuff as well. Source: 1)

Imagine yourself submerged in the prehistoric ocean. There are no fish, instead the only life forms consist of feather-like sessile organisms that sit on the seabed, filtering the current. The early organisms that evolved out of this, such as Jellyfish and Starfish, had radial anatomy. Their body structure entails a central axis from which you can split everything else. These bodies are simple, not designed for active mobility, lacking a ‘forwards’ or ‘backwards’. They didn’t even have eyes, instead interacting with and responding to the world via photoreceptive cells. What emerged from this were two developments: the evolution of complex eyes and the emergence of bilateral anatomy in early vertebrates and arthropods. In contrast to radial anatomy, bilateral anatomy entails an organism that can be split down the middle with rough symmetry. This is to say that they are built for direction. A body that is built for mobility entails significantly more complex behaviour behind its operation. Behaviour, in this sense, also becomes significantly more directed. These creatures now living in the ocean or on the sea-floor now begin to directly interact with one another. The mechanisms facilitating this interaction become pretty apparent in the fossil record; eyes, claws and antennae. The evolutionary consequences of this are the emergence of a complex nervous system alongside the presence of predation and, as Godfrey-Smith puts it “[From this point on] The mind evolved in response to other minds”. 

More Posts from Phoronopsis and Others

3 months ago

we all know people who go out of their way to be rude on bug appreciation posts are annoying as heck but sometimes they manage to read the room so absurdly poorly that it's just funny. You'll see a photo with 200 notes by someone called "flylover4ever" with the caption "look at this beautiful blowfly I found on my morning bug hunt 😊" and every comment note and tag is something like "look at that coloring!" "what beautiful eyes you have 😍" "KISSING HER ON THE TERGAL PLATE" and then there's just one rando person being like "EWWW kill it with fire 🤮". And it's like how did you even get here. are you lost, where did you even come from


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6 months ago
Pretty Princesses
Pretty Princesses

pretty princesses


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6 months ago

This crab is under construction! Read more on the Aquarium's website. 🦀🦺

Caring for Crustaceans with Creativity
aquariumofpacific.org
An aquarist cares for crabs in need of new shells in a new, inventive way, by using non-toxic epoxy, molding, and paint.

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8 months ago

Penis worms is serious business! been no-joke half-considering making an account to make a PSA about it (and other invertebrate stuff) for a while ^^; I like priapulids a lot, they’re a really underrated (and understudied) phylum

Hi, created an account just to let you know the photo you posted earlier is not a priapulid but a spawning sea cucumber, likely genus Paracaudina. It was misidentified on iNaturalist and went viral before it got corrected, and now it comes up on the search results along with a bunch of other worms like spoon and peanut worms that people misidentify as priapulids. The only priapulid that there’s good photos of is P. caudatus which is very distinctive if you know what it looks like. Love the blog!

Ah!!! Thank you very much for letting me know friend (even going as far as to make an account about it), sucks that these incorrect images have spread so far x(


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7 months ago

During the storm, I've had a wasp sheltering on my window.

It's been two days now, and she's still there, so I gave her some honey

During The Storm, I've Had A Wasp Sheltering On My Window.
During The Storm, I've Had A Wasp Sheltering On My Window.

Lookit her! slurping away!

@onenicebugperday


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1 week ago

Conch snails actually do have some of their own tricks up their shells— their foot bears a sharpened operculum that they use to push themselves around much faster than a lot of slow predators (including cone snails) can move, or even to fight back. It's believed that their high-resolution vision, which is some of the best among all known gastropods, allows them to detect and react to predators in advance (source 1, 2)

Here's a video of a conch snail in action:

How Are Conchs Even Real

How are conchs even real


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7 months ago

me walking up to the whalefall: hey my fellow hagfish hows it slimin' hagatha (she's a hagfish): are you sure you're a hagfish? you look kinda like some kinda lungfish me: haha dont worry check this out (i breathe in some pollen) HURHUHUHHHUUUURURGURGUGRGG hagatha: yep, that's a hagfish-y amount of slime. come hag out! (hagfish for hang out)


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3 months ago

also I want to append to this, we shouldn't necessarily assume that animals will be like humans; in scientific research you want to be careful with your preconceptions and personal biases, and in dealing with animals in person over-anthropomorphizing them can even be dangerous, for you and for them. But I think dismissing it out of hand in the other direction is just pretty ignorant given all the things we do know and all the things we know we don't, dubious from a moral perspective (if a creature looks like it's in pain, uh should not the null hypothesis be that it is in pain?), and stems from a really anthropocentric philosophy that has plagued even certain areas of biology itself (if you've read about like, human brain evolution you know what I mean) in a way that is soo frustrating and just is like, augh stop the ghost of Aristotle haunts you

Also I picked those fruit fly examples because they demonstrate ways in which insects are like us, but there's also by no means anything lesser about animals or other organisms that aren't like us either! Not everything is going to be like us and I think there's value and respect-worthiness in that too.

also there's evidence that white garden snails can distinguish numbers up to five

It's always so weird to come down from the biology heavens to see what the average person believes about animals, plants, ecosystems, just the world around them. I don't even mean things that one simply doesn't know because they've never been told or things that are confusing, I'm talking about people who genuinely do not see insects as animals. What are you saying. Every time I see a crawling or fluttering little guy I know that little guy has motivations and drive to fulfill those motivations. There are gears turning in their head! They are perceiving this world and they are drawing conclusions, they are conscious. And yet it's still a whole thing if various bugs of the world feel pain or if they are simply Instinct Machines that are Not Truly Aware of Anything At All????? Help!!!!!! How can you look at a little guy and think he is just the macroscopic animal version of a virus


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3 weeks ago

been getting really into rockhounding lately and the subreddits are great

Been Getting Really Into Rockhounding Lately And The Subreddits Are Great

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phoronopsis - actinotroch
actinotroch

they/she ✩ I like space and invertebrates

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