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  • "Stories from the Sea"

  • "Urchin Odyssey: Sex Among Plankton"

  • I must look rather strange to you,

  • all covered in spines,

  • without even a face.

  • But I've taken many forms during my life.

  • I started out just like you,

  • a tiny egg in a watery world.

  • My parents never knew each other.

  • One moonlit night before a storm,

  • thousands of urchins, clams and corals

  • released trillions of sperm and eggs into the open sea.

  • My father's sperm somehow met my mother's egg,

  • and they fused.

  • Fertilization.

  • Instantly, I became an embryo the size of a speck of dust.

  • After a few hours of drifting,

  • I cleaved in two, then four,

  • then eight cells. Then so many I lost count.

  • In less than a day,

  • I developed a gut and a skeleton.

  • I became a rocket ship,

  • a pluteus larva.

  • I floated through the world of plankton,

  • searching for tiny algae to eat.

  • For weeks,

  • I was surrounded by all kinds of organisms,

  • larvae of all sorts.

  • Most are so different from their adult form

  • that biologists have a tough time figuring out who they are.

  • Try matching these youngsters to their parents.

  • This veliger larva

  • will turn into a snail.

  • This zoea, into a crab.

  • And this planula into a cnidaria jelly.

  • Some of my young companions are easier to picture as grown-ups.

  • These baby jellies, known as ephyrae

  • already resemble their beautiful but deadly parents.

  • Here in the plankton,

  • there's more than one way to get your genes into the next generation.

  • Most medusa jellies

  • make special structures called polyps

  • that simply bud off babies with no need for sex.

  • Salps are similar.

  • When food is abundant, they just clone themselves into long chains.

  • A plankton is full of surprises when it comes to sex.

  • Meet the hermaphrodites.

  • These comb jellies and arrow worms

  • produce, store and release both sperm and eggs.

  • They can fertilize themselves

  • or another.

  • When you're floating in a vast sea,

  • with little control over who you may meet,

  • it can pay to play both sides of the field.

  • The majority of species here, however,

  • never mate, nor form any sort of lasting bonds.

  • That was my parents' strategy.

  • There were so many of us pluteus larvae,

  • I just hid in the crowd while most of my kin were devoured.

  • Not all parents leave the survival of their offspring to chance.

  • Some have far fewer young,

  • and take much better care of them,

  • brooding their precious cargo for days, even months.

  • This speedy copepod

  • totes her beautifully packaged eggs for days.

  • This phronima crustacean carries her babies on her chest,

  • then carefully places them in a gelatinous barrel.

  • But the black-eyed squid takes the prize.

  • She cradles her eggs in long arms for nine months,

  • the same time it takes to gestate a human infant.

  • Eventually all youngsters have to make it on their own in this drifting world.

  • Some will spend their whole lives in the plankton,

  • but others, like me, move on.

  • A few weeks after I was conceived,

  • I decided to settle down

  • and metamorphosed into a recognizable urchin.

  • So now you know a bit of my story.

  • I may just be a slow-moving ball of spines,

  • but don't let my calm adult exterior fool you.

  • I was a rocket ship.

  • I was a wild child.

"Stories from the Sea"

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B2 TED-Ed plankton sperm larva urchin drifting

【TED-Ed】How life begins in the deep ocean - Tierney Thys

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    Carol Chen posted on 2013/03/17
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