In case U missed it...'Strange Findings on Comb Jellies Uproot Animal Family Tree'

"It's a paradox," said Leonid Moroz, a neurobiologist at the University of Florida in Gainesville and lead author of a paper in today's Nature about the biology of the comb jelly nervous system. "These are animals with a complex nervous system, but they basically use a completely different chemical language" from every other animal. "You have to explain it one way or another."

The way Moroz explains it is with an evolutionary scenario—one that's at odds with traditional accounts of animal evolution.

Rewriting Evolutionary History

The unique nature of the comb jelly nervous system led the Florida scientists to hypothesize a new evolutionary history for these marine animals, which they laid out in the Nature paper. The earliest animals, according to this new theory, had no nervous system at all. The cells of these early animals could sense their environment directly, and could send signals directly to neighboring cells.

Millions of years later, those signals and receptors became the raw material for the nervous system. But its evolution, according to Moroz, took place in two separate lineages. One led to today's ctenophores. The other led to all other animals with nervous systems—from jellyfish to us.

Moroz and his colleagues have been studying comb jellies, whose scientific name is ctenophores (pronounced TEN-o-fors), for many years, beginning with the sequencing of the genome of one species, the Pacific sea gooseberry, in 2007. The sea gooseberry has 19,523 genes, about the same number as are found in the human genome.

The scientists enlarged their library to the genes of ten other species of comb jelly (out of the 150 or so species known to exist) and compared them to the analogous genes in other animals. And when they looked at the genes involved in the nervous system, they found that many considered essential for the development and function of neurons were simply missing in the comb jelly.

Some of those missing genes are involved in building neurons in embryos. The cells in any animal start out in the embryo as stem cells, looking pretty much identical to one another and capable of turning into any particular type of cell. Only later in embryonic development do some stem cells switch on specific genes that transform them into neurons. This process is much the same in humans as it is in flies, slugs, and just about every other animal with a nervous system.

But comb jellies, Moroz and his colleagues found, lack those neuron-building genes altogether. Which means that comb jelly embryos must build their neurons from a different set of instructions—instructions no one yet understands.

Nor do comb jellies use the standard complement of neurotransmitters found in other animals, the scientists found. The genes for most of the neurotransmitters in other animals are either missing or silent in the comb jelly—except for one, the gene for the neurotransmitter glutamate. No wonder Moroz likes to call these creatures "aliens of the sea."

http://news.nationalgeographic.com/news/2014/05/140521-comb-jelly-ctenophores-oldest-animal-family-tree-science/

------------------

In other words, they can repair and replace their brain cells, and entire brains.


Comb Jellies Show there is More than One Way to Make a Brain

Comb Jellies (belonging to the phylum Ctenophora) are fascinating; they can regenerate not only body parts, but also their brains. These organisms show that there is more than one way of making a nervous system.

http://www.natureworldnews.com/articles/7182/20140522/comb-jellies-show-more-one-way-make-brain.htm