So far, it has been the opinion of the majority of researchers that the nervous system of animals evolved all at once, after sponges without a nervous system separated themselves from the rest of the animal kingdom, as he writes: Life Science.
The mystery of the finned jellyfish
Others believe that ctenophores, or fin jellyfish, are a separate class that diverged early from other animals and developed their own specialized nervous system. Its first specimens may have appeared on the western shores of the Atlantic Ocean 540 million years ago.
They don’t have brains, they have neural networks with embedded neurons. The majority of their neurons communicate through synapses, for which neurons release neurotransmitters.
New research has proven that within the neural network of jellyfish in the form of a rib, cells merge and their membranes connect, so that the path from cell body to cell body is continuous, and this is the creature (a cell unit that contains several nuclei, cells that flow into each other without a cell wall) .
There are other animals with fusion neurons, but they are not complete neural networks. This unique arrangement may support the fact that their nervous system evolved separately from other animals. However, according to the researchers, it is also possible that all animal nervous systems had a common ancestor, and that jellyfish evolved their specialized cell fusion only much later.
The single common ancestor of all animals may have been a multicellular organism that may have lived more than 600 million years ago. This ancestor had two descendants: one that led to the evolution of all animal life, and the other that may have been sibling to all animals today.
So far, researchers have had two main candidates for the position of sibling – sea sponges and jellyfish – but have not been able to prove the hypotheses. Darren T. Schultz, a postdoctoral researcher at the University of Vienna, is the author of the new study, in which the genomes of jellyfish and their close relatives were sequenced, but instead of comparing individual genes, the team examined the chromosomal position between species.
As in the card
During development, changes occur in the DNA, but the genes usually remain on the same chromosome. In the rare cases that genes combine or mix, they can be passed from one chromosome to another in an irreversible process. Schultz compares this to shuffling two decks of cards, which can almost never be separated again as they were originally:
That is, if a gene is transferred from one chromosome to another, there is almost no chance that it will reappear at its original position later in development.
The team found 14 sets of genes that appeared on separate chromosomes in jellyfish and their single-celled, non-animal relatives. Interestingly, in sponges and all other animals, these genes are arranged into seven groups. The rib-shaped jellyfish DNA keeps the gene clusters in place (before rearranging into the seven clusters), indicating that they are descendants of a sister group that split off the animal’s family tree before admixture.
Gene rearrangements, which were common to both sponges and all other animals, point to a common ancestor from whom these rearrangements were inherited.
