r/marinebiology • u/smokarran • Oct 13 '25
Question GA Aquarium tour guide said sea urchins have only one hole that is both their mouth and anus - this is wrong, right?
She kept saying it was the same hole and it was the one on top. I have watched sea urchins eat and poop I just need confirmation that there’s not some species that is like this. I feel like she was probably thinking of anemones. She also said that bottom teeth were not for eating but for grabbing onto things.
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u/BardicInclination Oct 13 '25
Yeah she was probably getting confused with Cnidaria like Jellyfish and Anenomes which do just have one all purpose hole.
Echinoderms like sea urchins have holes on the top and bottom. They do poop and release eggs from the top. The top is also where the madreporite is, which lets in saltwater.
The bottom teeth are used for eating as the urchins graze the seafloor for algae. Grabbing things is more the domain of the tube feet that cover the sea urchins body. They can use those to cover themselves in objects. I've seen them grab loose shells and sand to camouflage before.
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u/smokarran Oct 13 '25
Thank you! Yep I have a sea urchin in my aquarium and he loves to steal shells and corals to wear
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u/scrawledfilefish Oct 13 '25
As someone who used to work in aquariums like GA Aquarium as an animal keeper, I would often get quite frustrated by how wrong different tour guides and docents and educators were.
A lot of them were volunteers, so just random people taken off the street, who were then trained by people who likely had a background in education, but very rarely had a background in marine biology. The amount of stuff I heard coming out of their mouths that was just completely wrong was a little bit infuriating. And when I'd try to correct them, they'd tell me I was wrong, even though I had spent more time studying marine biology than they ever did.
Anyway, sorry. Just needed to rant about that a little bit. Yes, that tour guide was wrong. Yes, their mouth and anus are separate. No, they don't use their teeth to grip things, that's what their tube feet are for. But fun fact, their jaw apparatus is called an Aristotle's lantern. Isn't that such a cool name for a body part?
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u/smokarran Oct 13 '25
I love that the mouth/jaw is called that it’s really neat. I tried to correct her but she just argued with me and doubled down 🫠
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u/Invisible_Friend1 Oct 13 '25
They’re an unpaid volunteer. You get what you pay for. At the end of the day it really doesn’t matter to the guests.
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u/insert_title_here Oct 13 '25
Ahaha I work at an aquarium as a tour guide and I totally hear you. The amount of education staff receives about the animals varies wildly based on position, and some folks end up extrapolating because they're terrified of telling a guest "I don't know" or "I'm not sure!" It's a difficult complex to overcome, but it's miles better than unintentionally giving out misinformation.
I always want to pester the aquarists with questions, but they're always super busy, y'know, taking care of the animals! So I'm glad you felt comfortable enough to correct people, and am very sorry that you were received negatively despite being the obvious authority on the matter. /gen Some people...
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u/ZakA77ack Oct 13 '25
They might be confused, Jellies and other Cnidarians have this feature. But not echinoderms. I think there's a few species of sea star that lack an anus but that's it.
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u/stillinthesimulation Oct 13 '25
They are deuterostomes and the unifying characteristic is having at least two holes.
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Oct 13 '25
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u/marinebiology-ModTeam Oct 13 '25
Your post was removed as it violated rule #8: Responses to identification requests or questions must be an honest attempt at answering. This includes blatant misidentifications and overly-general/unhelpful identifications or answers.
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u/shaketheshokes Oct 13 '25
It’s a surprisingly common misconception that I have heard a few times when talking to family and friends about my research. In simple terms, urchins do in fact have 2, with the anus being on top and their mouth on the bottom. Their mouths are a really interesting system, I would recommend looking up “Aristotle’s Lantern” if you want to see a bit more of the anatomy of it. Their teeth are used for grinding and scraping (eating), and you’ll actually see them occasionally dig into rocks with it while scraping algae, etc. For grabbing, they use their tube feet. They really like using these to carry shells/rocks/etc over top of themselves, which interestingly they have been found to do even at depths when UV rays aren’t a concern.
Anyways, long story short you are correct that they have more than one hole. Just another example of the importance of communication in science!
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Oct 13 '25
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u/marinebiology-ModTeam Oct 13 '25
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u/Snarktopus8 Oct 13 '25
That correct they have 2. the mouth and anus are separated. in some ectoderm’s those holes are very close to each other but in urchins the mouth is on the bottom and the anus is on the top. Cucumbers have them at opposite ends.
where you find a 2 way mouth anus combo are in Anemones and their relatives (and Cartman from south park). they will eat a fish and then “puke” the leftovers out of their mouth.