The heartbreaking beauty of development

This is a spectacular video of the development of Clypeaster subdepressus, also called a sand dollar or sea biscuit. These are stunningly beautiful creatures (as are we all, of course), and it is so cool to see them changing here. The video starts with a little echinoderm porn — these animals are profligate with their gametes — and then we see early divisions, gastrulation, the formation of the pluteus larva, metamorphosis into Aristotle’s lantern (one of the more charming names for a developmental stage), and into an ungainly spiky juvenile.

This is why some of us are developmental biologists: it’s all about the exotic weirdness and delicate loveliness of transformation.


  1. says

    This is why some of us are developmental biologists: it’s all about the exotic weirdness and delicate loveliness of transformation.

    The way so much history is written into it is cool, too. I had one creationist teacher who wanted to change taxonomy to reflect adult forms, probably because he was embarrassed at the strange “design” of making similar adults via dissimilar larvae (except that the larvae are similar to dissimilar adults).

    It’s not a happy pursuit for those who look for design that isn’t there.

    Great little film, btw.

    Glen D

  2. sjburnt says

    Thanks for posting. I really appreciate this sort of thing. I never had an idea what the animal looked like, other than the ubiquitous dollars on the beach.

  3. says

    Awww… that was cute. It was also very beautiful.
    Not as cute as the octopus in a clam shell but much more beautiful and fascinating.

    Not sure if I am unusual in this respect but I could watch films on nature all day long and never get bored. :shrug:


  4. Janine ID AKA The Lone Drinker says

    Cool. But I have a smart ass question. Is there any echinoderm porn where one of the sea biscuits is a pizza deliverer?

  5. Curt Cameron says

    I had no idea that “sea biscuit” was another name for sand dollar. I thought the race horse just had a name of two things stuck together.

  6. David Marjanović, OM says

    No, Aristotle’s Lantern is not a stage in development. It’s the mouth apparatus with the five “teeth”. That’s why a subtitle in the video says “Aristotle’s Lantern of the juvenile”.

    I love the glitchy music.

    It’s way too loud. It distracts from the film :-)

  7. Shane says

    I don’t know. That beginning was a bit explicit. We really need a filter on the internet to keep this kind of smut away from our children.

    Seriously, though, the kind of worlds that exist out there beyond our regular perception are fascinating.

  8. Nick Gotts says

    “Distant cousins: there’s a limited supply!” – Captain Beefheart

    Ha! Keep your slimy cephalopods! Deuterostomes rule!

  9. Diego says

    Aristotle’s lantern isn’t a developmental stage. It’s the really cool feeding apparatus of echinoids. The slide clearly indicates that the label is part of the larva, not the larva itself.

  10. Mus says

    he he he… I feel so smart now. I actually knew what Aristotle’s Lantern was… and PZ didn’t!

    That’s so great.

    The video is AWESOME too.

  11. says

    Wow, that’s absolutely fascinating and amazing photography, too. I really found gastrulation ultra-cool; I’ve read about it, but this helped me “get” it. I wish there were more time with gastrulation, though.

  12. says

    excuse my ignorance…

    I got the egg laying thing, i got the sperm thing…was that on the same sand dollar? or was that two different sand dollars?

    What was the needle in the beginning for?

  13. John Scanlon FCD says

    Very beautiful in parts, but the metamorphosis reminded me of the unnatural flesh-bubbling transformations in Altered States or the second Harry Potter film.

  14. JM Inc. says

    Awsome video. Awsome subject. This is why biology is so cool. I personally like the brain – it’s like development on steroids all the time (in terms of all the mind-bending stuff that happens).

  15. Brine Queen says

    @ techskeptic:

    Two different sea biscuits. The needle in the beginning was probably full of KCl, which is used to induce spawning in many echinoderms (sea urchins, sea stars, etc.). You can’t tell if it is a male or a female until it starts leaking gametes, so they most likely injected several sea biscuits, until they got a male and a female releaseing.

  16. mayhempix says

    Loved the post metamorphic juvenile with the punk haircut.

    And that was the longest cum shot I’ve ever seen… I wonder when Bill Donohue will condemn it claiming it discriminates against Catholics and violates his rights. Of course he’s just jealous.

  17. says

    Thanks Brine Queen!

    I felt stupid asking it, but I’m no biologist and I have heard of some animals that don’t need a male.

    has there ever been a post by PZ (or anyone) on how the hell some life forms became sexual creatures and some can undergo parthogenesis? Why is parthogenesis rare? I guess I am asking what the evolutionary steps were that we think developed sexes (and yes I fully know that I am sounding troll like here, it wont be the first time, probably wont be the last, i’m just trying to fill the spiderweb ridden area of my brain that once contained biology)

    I never expected a sand dollar to be a sexual creature.

  18. Owlmirror says

    has there ever been a post by PZ (or anyone) on how the hell some life forms became sexual creatures and some can undergo parthogenesis? Why is parthogenesis rare?

    There’s a chapter in The Ancestor’s Tale by Richard Dawkins, which discusses parthenogenesis, and I seem to recall that he says that how it arises is still unknown and argued over.

    And while parthenogenesis is indeed rare in most multi-celled life forms, it is surprisingly common in bdelloid rotifers; I think there is a study which analyzes the X chromosomes of rotifers which indicates that they have been reproducing that way for a very long time.

    Anyway, it’s an interesting chapter if you’re interested in the topic.

  19. CanadianChick says

    Wow – I watched that, mouth hanging open, and remembered what it was about science that had interested me many moons ago (a path I chose not to take)…

    that was fascinating, beautiful, and just plain freakin’ cool!

    And thanks techskeptic for asking that question, and Brine Queen for answering it, and PZ for posting the video…


  20. John Phillips, FCD says

    WOW, just, WOW.

    ’til the day I die I will never tire of the wonders of this universe, or if I ever do I might as well be dead.

  21. noncarborundum says

    So the larvae seem to have bilateral symmetry (2, 4 and 8 arms), but the adults have 5-fold radial symmetry and so, to judge from their Aristotle’s lanterns, do the juveniles. I’d love to have some idea how & why this happens. Does anyone know?

  22. Jim Thomerson says

    That Aristotle’s lantern is the set of “teeth” of an echinoderm is part of the common knowledge of all educated people. However, I wondered if, as PZ implied, it also is used in reference to the developmental stage in which Aristotle’s lanter is formed. That doesn’t seem unreasonabe. However, I googled around in inquiry and am now wiser than I was before.

  23. says

    thanks for posting it, pz!

    @David, Diego, and Mus: indeed, the Aristotle’s lantern is the mouth apparatus of sea urchins and sea biscuits ;-)

    @Bardiac: yes, gastrulation was a bit quick and I had to use photos, since larvae during gastrulation swim like crazy little kids, making it difficult to shoot them continuously over time (they only stop if you glue them to the slide)

    @techskeptic: thats exactly as Brine Queen explained :-)

  24. chgo_liz says

    This being Pharyngula and all, everyone is aware that the sand dollar is considered a christian symbol because the 5 points of the star symbolize his wounds on the cross, right?

    There’s a horrible, saccharine “poem” about it, if anyone’s interested. (No, really, you aren’t.)

  25. Snoof says

    This being Pharyngula and all, everyone is aware that the sand dollar is considered a christian symbol because the 5 points of the star symbolize his wounds on the cross, right?

    Hasn’t practically everything in the entire universe been co-opted as a Christian symbol nowadays? Lions, sheep, crosses, stars, trees, boats, rainbows, eggs… the list goes on.

  26. Blind Squirrel FCD says

    #38 The organism you are referring to is the 5 hole keyhole urchin. Sand dollars have no keyholes.

  27. Hanspeter says

    First thing I thought was that the researchers needed a microscope w/ a bigger depth of field :)

  28. Peter Ashby says

    A quick check with New Scientist confirms my memory that some bdelloid rotifers haven’t had sex for around 70million years. They seem to have a genome that is remarkably resistant to mutation. But that is the mechanism of how you do without sex for that long, it doesn’t tell you why, what pressures are/were present/absent in their environment that pushed them/released them into/from asexual/sexual development. it’s intimately related to the problem of why have sex at all? Some creatures, aphids for eg mix and match depending on conditions, when a female lands on your roses she can’t sit about waiting for a male to wander past. There’s a whole rose to colonise, so she spits out parthenogentic copies at a great rate. Time for sex later.

  29. says

    Bruno [37], Welcome! How nice to have the researcher show up to answer comments!

    That was fascinating. Any chance of a series of diagrams showing gastrulation and the metamorphoses, especially from bilateral to pentameral? Or is that covered in the Big Book of Echinoderms somewhere?

    Thanks so much for publishing this.

    David M [13], you have a volume control, don’t you? :-)

  30. farinosa says

    Those are the cutest little tube-feet ever! Once past the pluteal stage, echinoderm toddlerhood is such a joy. But, they get into everything.

  31. Bodach says

    Like everyone else said, Cool & Wow!, etc. I need a follow up showing the juvie becoming an adult. How’s the shell built up, etc.?

  32. says

    You’ve gone and made me learn something – I had to look up what the hell a seabiscuit actually was o.o Personally, I prefer nudibranchs when it comes to interesting sea creatures c.c terribly facinating video though – I’ve always enjoyed seeing the developmental stages

  33. Sili says

    “Espermatozoa” makes me smile …

    I don’t think I’ve seen a sand dollar (or heard of them). But I think I’ve been to the beach less than a handful of times. (More often than I’ve been to the cinema, though.)

  34. says

    @noncarborundum[#35]: that’s a very good and difficult question! It looks like, considering recent data on gene expression and developmental patterns, that what we call pentamerous symmetry is “just” a “disguised” bilateral symmetry. I know this does not explain how and why it happens, but shows how much we still need to uncover to understand echinoderms. There are some articles about that, if you are interested.

    Just a point to clear out, adult sea biscuits/sand dollars have bilateral symmetry (although they look pentamerous).

    @chgo_liz[#38]: I keep forgetting this… :-P

    @Monado[#44]: Hello! You can find diagrams of echinoderm development on big books. Not sure how much detail you want.

    @Bodach[#46]: The skeleton is made of fused tiny calcarious spicules secreted by some cells.

    Thanks so much for the comments!

  35. karen marie says

    those little sea biscuits are so darned cute!

    and the music in the video was excellent.


  36. OctoberMermaid says

    I couldn’t follow that video at all.

    I mean, the part with the cleavage was hot, but then all of a sudden we’re seeing videos of Sputnik or something? Man, if that’s what you’re into, that’s cool, but I wouldn’t raise a Communist flag, so I’m not raisin’ anything else for those Commie slimes!