non-ceph: starfish reproduction

Discussion in 'Physiology and Biology' started by monty, Apr 20, 2008.

  1. monty

    monty Colossal Squid Staff Member Supporter

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    I pretty much have no clue, but I can confirm that most starfish (and echinoderms in general) reproduce sexually and have a planktonic larval stage. Starfish can regrow severed limbs, and I think some research was done in terms of how much of the middle you need to re-grow, but my recollection is that you need more than half of the middle to be viable. There was a paper in the last month or so about ago about sand dollar larvae being able to bud: http://www.columbusdispatch.com/liv...llar.ART_ART_04-01-08_B5_V29P5DQ.html?sid=101
    Note, though, that the larva looks nothing like the adult animal, and is a whole lot smaller, so this wouldn't explain your starfish. Are you sure they're actually starfish and not some other sort of critter? I can't really tell from the picture. I think there are some weird mutant species of Starfish that has 6 arms, but almost all have a 5 or a multiple of 5 (like sun stars).
     
  2. cuttlegirl

    cuttlegirl Colossal Squid Supporter Registered

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  3. cuttlegirl

    cuttlegirl Colossal Squid Supporter Registered

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    :bonk: I just found out that there is an Asterina species that is ovoviviparous, meaning that development takes place inside the adult and then the fully formed juveniles are released from the adult. I am not sure if that is the same species that you have.

    http://www.jstor.org/pss/1542316
     
  4. monty

    monty Colossal Squid Staff Member Supporter

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    Weird/cool. I can only read the abstract, but I think I get the point. Very odd... I should really learn to never accept any generalizations in biology. And it looks like the Asterina found in aquariums commonly also has a very wide variation in number of arms, which is curious, since I found other references that made a big deal about how HOX genes and developmental weirdness account for populations of 6-armed starfish and 4-symmetric urchins, yet they didn't suggest that populations of starfish with a random number of arms from 3 to 6 would exist. I wonder if this is a developmental thing, or perhaps if, since apparently the abstract describes direct developing starfish (so I was wrong about the generalization about a larval stage) if they develop 3 legs first and then grow the rest, or something.

    I thought that the "normal" developmental process for echinoderms was that a fertilized egg develops into a blaterian larva with some "set aside" cells that will become the adult, then the larva feeds to provide nutrients for the developing adult, until the adult wraps around (I forget if it's head-to-tail or left-to-right to transform into a radial adult) and eats the remaining larval bits. The sea urchin genetics people seem to not mention that there are weird outliers to this... although maybe that's just because there's plenty of controversial weirdness in the supposedly-well-studied sea urchins.

    This seems interesting, too:

    http://www.springerlink.com/content/n704g233g7431443/

    apparently being an example where the "larva" is a "cilliated blastula" :bonk:

    I think I'll split the stuff not-so-relevant to the original question into physiology and biology to reduce (or induce?) confusion.
     
  5. Jean

    Jean Colossal Squid Supporter

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    Some Stars are fissiparous, they reproduce by breaking apart. One of the ones in the pics looks to be doing just that, 3 arms on either side of a stretched out central disc. We have one here that we call the three and three star (Allostichaster insignis) because this is it's main mode of reproduction and we often have 3 armed stars (well actually stars with three big arms and three little ones!) in the aquarium tanks!

    J
     
  6. monty

    monty Colossal Squid Staff Member Supporter

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    I continue to be astounded at how many generalizations I read about or learned about in high school biology turn out to be completely wrong...

    Do you know what happens morphologically as they split? I'm pretty sure (insofar as I'm sure about anything about echinoderms now) that the adult body plan is head-to-tail linked in a circle-- do they split midway into a new head-and-tail and make to daughter "loops"? Or unzip down the midline? or something else-- I can't think of a way to grow another whole proto-adult and pass 3 arms off to the child, but at this point I wouldn't be surprised by anything...
     
  7. Jean

    Jean Colossal Squid Supporter

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    Ours unzip down the middle and then the side with no arms proceeds to grow new ones. I hadn't heard the head to tail linked in a circle description before. I understood them to have a non centralised nervous system and to be generally penta-radial around a central disc (some have secondarily modified this!), so that they can respond in any direction...............???????


    J
     
  8. monty

    monty Colossal Squid Staff Member Supporter

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    Well, I'm starting to question everything I've read about them... this is particularly surprising, since I sat in on a class that used sea urchin embryos as the model system for gene regulatory networks for development... but it was more about the larval than adult form.

    This random site on the intenet says:

    This is a bit more credible-sounding:

    This abstract would seem to indicate that it's complicated and still an area for active research...

    and this one intimidates me with big words:read::goofysca::bonk: (pdf version at http://icb.oxfordjournals.org/cgi/reprint/38/6/965.pdf )

    there's a glossary of echinoderm terms here: http://www.dnr.sc.gov/marine/sertc/Echinoderm glossary.pdf

    I think I'll leave this at :confused: and stop trying to read enough that this post is coherent, 'cause the more I read, the more confused I get...
     
  9. Animal Mother

    Animal Mother Architeuthis Supporter

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    I witnessed a spawning event a while back with my tiny brittle stars. Was quite interesting. They all came out at the same time, everywhere in the tank... like there was some sort of signal. Then they all climbed to the highest nearby spot and started spewing their reproductive juices into the water column. It was over in about 15 minutes.

    I actually saw a larger 2 legged brittle star with a mangled disc climbing around in the seahorse tank a while back. Never saw the other half though. Don't know if it was intentional fission or if maybe I crushed the other half moving rocks around.

    I don't think any two asterina stars look the same. Very rarely do I see a 5 legged one.
     
  10. monty

    monty Colossal Squid Staff Member Supporter

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    from this overview (restricted access): http://linkinghub.elsevier.com/retrieve/pii/S0960982205014016

    so it sounds like wherever I got the idea that the head-foot became a loop was wrong. I'm almost positive that some book I read in the UCLA medical library said this, though... maybe it was some old theory that turned out to be wrong...
     
  11. Jean

    Jean Colossal Squid Supporter

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    There is quite a bit of work still to be done on this, we have a couple of researchers in our department working on echinoderm reproduction and other stuff such as UV protectants in the larvae in Antarctica (one of them is my Boss!).

    Old books are so much fun! I have an 1899 Zoology text which claims to have between it's pages all the information a student or professional scientist will ever need on all members of the animal kingdom, there is nothing left to learn (all this in one volume of some 600 pages!). some of the misconceptions are hilarious as are the descriptions of various species, Peripatus for example has skin of velvet, eyes like diamonds and exquisite antennae, it goes on to wax evermore lyrical, I just can't remember the details!

    J
     
  12. cuttlegirl

    cuttlegirl Colossal Squid Supporter Registered

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    When one echinoderm starts spawning it can trigger all the same species in the area to start spawning too. Sometimes if the temperature in the tank rises, it can cause a spawning event.

    Brittle stars quite a bit different from other stars, they don't reproduce by fission, so it must have been caused by some injury.
     
  13. Animal Mother

    Animal Mother Architeuthis Supporter

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    Thank you for clarifying that..... oops. What about serpent stars? Fission or no? I assume they are very similar to brittles.

    Either way, I have seen several of both in my tanks that have 6 legs, usually one leg shorter than the rest.
     
  14. cuttlegirl

    cuttlegirl Colossal Squid Supporter Registered

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  15. cuttlegirl

    cuttlegirl Colossal Squid Supporter Registered

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    It's not so bad after the abstract, if I ever have time, I will read the whole article. My favorite part...

    and 8 pages of text follow - abbreviated??? :bonk:
     
  16. Jean

    Jean Colossal Squid Supporter

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    depends on the species Ophiactis can, as can some others. Weirdly even some holothurians (sea cucumbers) can.

    J
     
  17. cuttlegirl

    cuttlegirl Colossal Squid Supporter Registered

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    :grin: Wow, you learn something every day...
     
  18. Jean

    Jean Colossal Squid Supporter

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    yeah, I learned this from my Boss who came in just as I was reading the post :oops: At least this forum is Marine related (no it wasn't lunch time, it was in work hours, tsk tsk).

    J
     

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