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‘Mind-Blowing’ New Creature Discovered

May 21, 2008

Among the
greatest mysteries in zoology for more than a century have been vaguely
shrimp-like creatures known as y-larvae.

Although
these microscopic beasts are clearly young crustaceans, no one knew what the
adult forms looked like.

Now
researchers may have solved this puzzle by dosing the y-larvae with a hormone
that forced them to go through a growth spurt.

The result
- simple, pulsing, slug-like
masses
of cells that were “mind-blowing” to the scientists. These surprisingly simple creatures – far simpler than their larval stage – may be
parasites found worldwide.

Dizzying diversity

Y-larvae,
or facetotectans, were first discovered in 1899. There were
once x-larvae as well, the ‘x’ and ‘y’ both denoting something mysterious.
Later on, the adult form of the x-larvae were found, but bafflingly, even after
intense searches, no one knew what y-larvae grew up to be, so they kept their
name.

These
critters are just a few hundred microns large, or roughly the size of the
period at the end of this sentence. They occur with dizzying diversity in coral
reef areas, and are found in all oceans, from the poles to the tropics. Their
commonplace nature suggests the adults play a major role in ecosystems around
the globe.

To find out
what these y-adults might be, an international team of scientists used nets to
collect more than 40 species of y-larvae from a marine station at Sesoko Island
near Okinawa, Japan. As they were gathering the
creatures, a cyclone
approached.

“It was predicted to hit the marine station five days
after the arrival of our team,” said researcher Henrik Glenner, a molecular biologist at the University of Copenhagen
in Denmark.
“This put us under substantial time pressure, because
we knew that it was impossible to catch the y-larvae after the cyclone had
passed. Therefore, we had to work during the nights.”

Safe back in the lab

The
researchers next exposed y-larvae to a crustacean hormone that encouraged them
to mature. The creatures
metamorphosized
into a juvenile form, dubbed “ypsigons,”
unexpectedly shedding their exoskeletons to become wriggling, eyeless, limbless
creatures that resemble parasitic crustaceans.

At first the researchers thought their eyes were tricking
them, but eventually “the juvenile literally crawled out of the old larval
carapace,” Glenner recalled. “It was only after several repeated
experiments we actually believed what we saw. That feeling was a mind-blowing
experience.”

The fact
that ypsigons are vastly different and far simpler than y-larvae might help explain
why the adult versions of these creatures have escaped detection for so long.
These are so simple compared with y-larvae that they even lack digestive tracts
and nervous systems.

Ypsigons
could make do without a digestive tract by directly absorbing nutrients from
their surroundings, They might develop a nervous
system later on in life, “but not necessarily,” Glenner said.

“I
know it sounds strange, but in some adult parasitic barnacles – rhizocephalans,
which parasitize other crustaceans – there are no traces of a nervous system
either,” Glenner told LiveScience.
“This is possible because their behavior as adults is restricted to
certain coordinated movements when they release their larvae.”

Probably parasites

As the
final adult stage of the y-larvae are probably parasites,
future efforts to uncover these y-adults – to solve this mystery once and for
all – will aim to identify their hosts by screening coral reef animals for y-larvae
DNA.

“These
parasites could play a very important role in the wild,” said researcher
Jens Høeg, a marine zoologist and invertebrate morphologist at the University
of Copenhagen in Denmark.
“They should not be seen as evil or bad. Wherever these parasites are, be
they in sea urchins or sea stars or corals, they are probably important in
making up what we consider a normal, healthy coral reef.”

Høeg, Glenner and their colleagues Mark
Grygier and Yoshihisa Fujita detailed their findings May 19 in the journal BMC Biology. They were supported by the
Carlsberg Foundation in Denmark
and the Lake Biwa
Museum in Japan.

 


Source: imaginova



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