Sep 12 2011

Mary’s Monday Metazoan: Sweet sessility

(via National Geographic)

(Also on Sb)


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  1. 1
    Glen Davidson

    Not very animated animals.

    OK, swimming as larvae, and a bit of “swimming” in the face of threat. Still put most couch potatoes to shame.

    Glen Davidson

  2. 2


    It reminds me a bit of “Evolution: The Story of Life on Earth” that you mentioned a while ago. It was terrific, so thanks for posting it.

    I can practically see Bloort 183 walking into frame to explain something interesting about the scene :)

  3. 3

    Why do you never post what these animals are? How are we supposed to go find out more about them if we don’t know what they are?

    Ooh, that sounded whiny, even to me. So let me just ask politely if you could, in the future, mention the name of the animals you feature, if it’s not too much trouble.


  4. 4
    Crip Dyke, Right Reverend Feminist FuckToy of Death & Her Handmaiden

    Okay, I just can’t look at those sea-pens and NOT think of the Ediacaran fauna.

    Do we have any good evidence one way or another for separate, convergent evolution of organisms like the sea pen? Or do we simply have long gaps in the fossil records of sea-pen like life, but the evidence that does exist is consistent with descent from pre-Cambrian days?

    Love to have someone knowledgeable on this piece of history step in.


  5. 5
    Crip Dyke, Right Reverend Feminist FuckToy of Death & Her Handmaiden

    In re: #3,

    The foregrounded creature is a sea pen (as I hoped was implied by my comment @ #4).

    In the middle background, in front of another sea-pen, is a vivid-blue cod … I *think* but am not sure. (It looks like a cod, but I don’t know how many other things might look like a cod).

    there is clearly a sea star in the background-right, but I can’t tell what else might be in the photo. Some shelled creatures might be there, a few corals, or maybe just some rocks and stuff.

  6. 6
    Glen Davidson

    Why do you never post what these animals are? How are we supposed to go find out more about them if we don’t know what they are?

    By clicking on the link. The answer’s usually there, though probably not always. Sometimes the picture’s the link, this time the word “National Geographic” is (below the picture).

    Most people know this, I think. Not faulting you for not, I’m just saying that I think that it’s not a mystery to most here how to find out the name and some facts most of the time.

    Glen Davidson

  7. 7

    Okay, I feel dumb. I thought the ‘via’ link just went to the main website (in this case, of National Geographic), and I never bothered to click through.

    Moral of the story: when in doubt, click everything. :-)

  8. 8
    Ron Sullivan

    All else aside, that’s a really interesting composition.

  9. 9

    NG says “They are rooted to the seafloor by an anchoring bulb—which can serve as sanctuary for the entire colony when threatened.” Which made me want to see that:


    It appears to be a slo-mo sort of deal, both going in and coming back out again. But if your predator is a slug, I ‘spect you have time.

  10. 10

    Are these really sessile? According to this video


    they drift along in the current.

  11. 11

    I’m pretty sure those are baby elderthings…

  12. 12

    All well and good but will these lovely creatures survive this toxic onslaught:



  13. 13

    In re: the age of this lineage — well, they’re cnidarians to start with, so they go way the fuck back. In particular, I think there’s at least one almost-definitely sea pen known from the Burgess Shale, so that puts you in the Middle Cambrian. Unfortunately things this squishy pretty much only fossilize under outrageously good circumstances like those of the Burgess Shale (i.e. Lagerstätten), so it’s a tricky problem.

    As far as the Ediacarans go, Charnia sure as hell looks like a sea pen in gross morphology, though its “colonies” are alternating rather than opposite, and look more quilted than feathered, which suggests that it might just be a convergent form…dunno.

  14. 14

    sessility is a sliding scale

  15. 15

    sessility is a sliding scale

    Really? I’m learning a lot from this post.

  16. 16

    Sure. Adult barnacles are glued down and hard corals are integrated into the very structure of a reef; they’re never going anywhere, whereas things like anemones and clams and these sea pens can actually move about a fair bit (albeit slowly).
    My favorite recent example was the crinoids called ‘sea lilies’ which were assumed to stay rooted in one spot (like so)…until this video was obtained!

  17. 17

    Being cnidarians, it certainly isn’t beyond the conceivable that Sea Pens might have had ancestors in the Ediacaran that already possessed a similar form. Though I think the Ediacaran critters that are known that look the most like Sea Pens are thought not to be in that lineage, but are convergent.

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