Anatomy Development Ecology Evolution

Ripping yourself out from the inside: The story of a starfish’s birth (and yours, too)

Baby starfish are actually magical ocean fairies called bipinnaria that swim whimsically through the sea:

Screen Shot 2018-08-26 at 4.26.21 PM
“Where’s the head, where’s the butt??”–said nearly everyone who saw this image. Screen cap from this video.

Yes, this wee young thing is a starfish, though it looks nothing of the sort. Starfish, like most animals, live a rather complicated life. We humans tend to think of life as very simple: born a little human, die a big old one. But for many animal kind, this is far from the case. Baby starfish, for example, start out looking like this:

But none of this crystalline ship will last. Because this body really is, in many ways, just a vessel for the starfish yet to form within.

As the bipinnaria filters and eats microscopic food, its body grows…and its internal organs and tissues do, too. All seems well to those of us who start out looking like small, somewhat misshapen versions of our adult selves (or so we like to think…), but when organs grow within a bipinnaria larvae, something strange happens. As soon as the larval body is big enough, one organ: the left coelomic pouch, begins to change, and the body of a baby star begins to form around it. As the tiny star grows, it sucks nutrients from the bipinnaria in which its forming. Growing heavier and heavier, the bipinnaria begins to sink. Once the weakened bipinnaria crashed to the sand, its now that the young star makes its move: using its tiny tube feet, it rips itself out of its old body; Sometimes even eating the shell of the bipinnaria that once carried it–it will need this vital energy from its own cannibalism to survive its first few days in this new form.

 

And while all this may seem alien, ripping out of your own body is a reality much closer to home. You did it, too.

The placenta and amniotic sac: the structures that cradled you in your mother’s womb, were formed from your own tissue. They were two of the first body parts you developed as an embryo, and they nourished you for the first nine months of your life. To be born, your current body had to pass through the shell of your old one: rupturing and then leaving the amniotic sac. And while you didn’t turn around and eat what remained of your former form, many mammal mothers do.

So while sea stars may seem odd, they are in fact a reflection of our own strange biology. Something to be admired, thankful for, and maybe even a little bit freaked out by. You’re missing a whole part of yourself you were once connected to. An organ that fed you, helped keep you clean–the first thing you grew in your life. When you think about it that way, metamorphosis doesn’t seem like such an alien concept after all.

 

4 comments on “Ripping yourself out from the inside: The story of a starfish’s birth (and yours, too)

  1. Love this post! The Daniel Brown animated development video was amazing! Beautiful! I love sea stars!! We have a pet Patiria here at Sunset Marine Labs! We’ve had him now for 12 years and he was at least a year old when he was given to us.

  2. landlockedmedusa

    Yet another extraordinary blog! Thank you for your incredible writing. Knowing next to nothing about vertebrates, I didn’t know that the placenta was made from the developing fetus – and I’m still turning that thought over and over in my mind.

    • Thanks–and to be totally honest, learning that was a shock to me, too! Like, what do you mean I’m missing this whole part of my body?!?!

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