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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.
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【TED-Ed】深海裡的火箭 How life begins in the deep ocean - Tierney Thys

4617 分類 收藏
Carol Chen 發佈於 2013 年 3 月 17 日
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