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Starfish: how do they work? - delta_november

Mar. 14th, 2011

08:46 pm - Starfish: how do they work?

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I have always been fascinated by zoological metamorphosis.  Some of you will have already heard me expound upon this theme.  In the metamorphosis of something like a caterpillar, we know that the structures of the larva do not turn into the structures of the adult.  For example, the caterpillar leg does not become the butterfly leg.  Instead, the animal inside the cocoon digests itself down into soup except for a few cells -- an egg, if you will -- that then grow back into a butterfly.

Some time ago I learned about Axolotl, and what happens if you inject it with iodine, and tripped most of the balls.  Today I've been reading about starfish metamorphosis.  It's fascinating.  I had known that the larva had bilateral symmetry, and the adult 5-fold radial symmetry.  So how does it change from one plan to another?  The larva is a fully formed animal, with a digestive tract and other organs.  When it has grown large enough, an area of tissue starts to grow into an adult starfish.  It has its own digestive tract, completely divorced from that of the larva.  Its other organs grow fresh, while the larva retains its own.  Finally the starfish drops off, leaving the larva swimming free!  Is your mind blown yet?  Mine is.  All the balls are tripped.

If you have yet un-tripped balls, here is an article that attempts to explain why this might be, and why so many animals with different adult forms have very similar larvae, while other closely related animals have no larval form at all.  It's a bold hypothesis.  Probably wrong, but if true our world is even stranger than we had thought.