Comb jelly

Brachiopod (2)
Coelenterate (129)
Comb jelly (60)
Invertebrate (64)
Sponge (73)
Starfish (22)
Worm (588)

Synopsis: 4.4. animals: Invertebrate: Comb jelly:

#Ctenophores Semaphore Information About Earliest Animals This article was published originally at The Conversation. The publication contributed the article to Livescience's Expert Voices:

Most of us have heard never of Ctenophores or comb jellies but this is about to change. In a publication out today in Science a team of researchers in the computational genomics unit at the National institutes of health in Maryland report that Ctenophora are the most ancient multicellular animals.

This was a spot previously held by sponges. To understand the implications of this finding we have to remember that multicellularity was a big step in evolution that occurred over 550 million years ago.

At the time there was an explosion of forms as life explored the limitations and possibilities of having a body made up of different types of cells.

and comb jellies) can be quite different at a genetic level. Modern taxonomy has embraced barcoding which uses the DNA sequence of a single gene to distinguish between closely related species

The breakthrough in today s paper is the sequencing of the entire genome of a Ctenophore known as the sea walnut (Mnemiopsis leidyi.

while the most ancient animals are the comb jellies. Ctenophores are delicate translucent creatures. They have eight rows of comb plates with cilia that provide them with locomotion.

They are carnivorous hermaphroditic marine creatures that do not sting. The sea walnut (M. leidyi) is native to the western Atlantic

but has been introduced to the Black Caspian and North seas where it has caused serious environmental and economic damage by eating native zooplankton and fish.

In terms of cellular arrangements Ctenophores have a nervous system and all three major cell types (endoderm ectoderm and mesoderm).

The sea walnut genome contained 16548 protein coding genes 44%of which shared homology-a type of ancestry-with non-Ctenophores.

For example Ctenophores have a nervous system and sponges do not but sponges do have required the genes for nervous system development and function.

Ctenophores however do have a third cell layer called a mesoglea which acts like muscle.

The earliest branch of the animal tree belongs to Ctenophora now confirmed to be the sister lineage to all other animals.

So don t confuse comb jellies with jellyfish. I think of the Ctenophores as a semaphore signalling some profound truths to us (in a blue green glow) across the vastness of time about animal origins and biological organisation.

Susan Lawler has received funding from the ARC in the past. This article was published originally at The Conversation.

Watson brought home some bioluminescent ctenophores (comb jellies) to show his wife then left them on the lawn.

and their tiny hairless bodies also lack the swimming cilia that define comb jellies another type of translucent ocean blob.

and the comb jellies even if we can't place them in either of those phyla. A phylum is a taxonomic group one level below a kingdom.

believe that Eoandromeda is the ancient ancestor of modern ocean dwellers known as comb jellies gelatinous creatures similar to jellyfish,

it would be known the oldest fossil of a comb jelly. And that would support a rewrite of the animal tree.

Comb jellies sit alongside two other major groups near the base of the tree, but their relative positions remain contentious.

followed by the cnidaria jellyfish, sea anemones and their kin and then by the comb jellies. Eoandromeda puts a little piece of weight in favour of a more basal position for comb jellies,

says Stefan Bengtson, a palaeontologist at the Swedish Museum of Natural history and a co-author on the paper.

This is in stark contrast to modern comb jellies, which, like humans, flies and sea anemones, have biradial

The proposal is in tune with DNA studies that place comb jellies closer to the root of the evolutionary tree.

His team recently sequenced the genome of the comb jelly Mnemiopsis leidyi, and is now comparing it to sequences from sponges,

and comb jellies appeared before cnidarians2. The matter is settled far from, however. Some scientists even doubt that the fossil is in fact that of a comb jelly.

The eight spiral arms are reminiscent of the eight iridescent rows, or combs, along the sides of modern comb jellies,

but the fossil lacks some key characteristics of modern comb jellies, such as tentacles and a mouth.

Differences between living animals and ancient fossils are expected, but the differences also allow for debate. Eoandromeda fossils are excellent and very important

Bengtson says he can't prove the fossil is a comb jelly but its comb-like arms indicate that it is one.

The only reason to suggest they are vendobionts, he says, is that they happen to be of that age.

Claus Nielsen, a retired evolutionary biologist at the Natural history Museum of Denmark in Copenhagen, doesn't think Eoandromeda represents comb jellies either.

Genome reveals comb jellies'ancient originanimals evolved gradually, from the lowly sponge to the menagerie of tentacled,

This idea makes such intuitive sense that biologists are stunned now by genome-sequencing data suggesting that the sponges were preceded by complex marine predators called comb jellies.

comb jellies form their own phylum, known as ctenophores. Trees of life typically root the comb jellies'lineage between the group containing jellyfish

and sea anemones and the one containing animals with heads and rears which include slugs, flies and humans.

Comb jellies paddle through the sea with iridescent cilia and snare prey with sticky tentacles. They are much more complex than sponges they have nerves, muscles, tissue layers and light sensors, all of which the sponges lack."

"It s just wild to imagine that comb jellies evolved before sponges, says Billie Swalla, a developmental biologist at the University of Washington in Seattle and a leading member of the team sequencing the genome of the comb jelly Pleurobrachia bachei.

But the team is suggesting just that, in results they presented at the annual meeting of the Society for Integrative and Comparative Biology,

Despite comb jellies'complexity, DNA sequences in the Pleurobrachia genome place them at the base of the animal tree of life, announced Swalla's colleague Leonid Moroz

Another team presented results from genome sequencing for the comb jelly Mnemiopsis leidyi, and found that the phylum lands either below,

"Now we need to imagine early life as a sponge, ctenophore and everything in between.

the ancestor of all animals might look different from modern comb jellies and sponges. Gene families, cell-signalling networks and patterns of gene expression in comb jellies support ancient origins as well.

For example, Moroz and his team found that comb jellies grow their nerves with unique sets of genes."

"These are aliens, Moroz jokes. He suggests that comb jellies might be descendants of Ediacaran organisms,

mysterious organisms that appear in the fossil record before animals. Indeed, in 2011, palaeontologists claimed that one of these 580-million-year-old fossils resembled comb jellies1.

Andy Baxevanis, a comparative biologist at the US National Human genome Research Institute in Bethesda, Maryland,

and a leader on the Mnemiopsis genome project, says that comb jellies are the only animals that lack certain genes crucial to producing microrna short RNA chains that help to regulate gene expression.

sponges and comb jellies lack other gene families that all other animals possess2, 3. If comb jellies evolved before sponges,

the sponges probably lost some of their ancestors'complexity. Alternatively, says Sally Leys, a biologist at the University of Alberta in Edmonton,

Sceptics wonder whether a high rate of genetic mutation in comb jellies might be causing the lineage to seem closer to the bottom of the tree than it really is."

"In the analyses I ve done, ctenophores are the most problematic taxon. They jump around depending on

Scientists found similarities between the organisms and members of Ctenophora and Cnidaria and suggest that they may be related to one of these phyla.

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