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In 2023, the ctenophore made a splash, surprising researchers at the С����Ƶ with its bizarre biology.  &�Բ�����;

Ctenophores, also known as comb jellies, are gelatinous invertebrates that beat their iridescent combs as they swim through the water. They’re an ancient animal, with over 700 million years of evolutionary history.  &�Բ�����;

Studying our oldest ancestor is like “looking into a window to the past,” said Oscar Arenas Sabogal, a postdoctoral scientist at the University of California, Berkeley, and Grass Lab associate director at С����Ƶ this summer. &�Բ�����;

For millions of years, comb jellies have brought with them an odd mix of parts and wiring – a physiology completely their own.  &�Բ�����;

With a body plan worthy of a “sea alien,” the organism seemed all the stranger when fellows at the Grass Lab gazed upon one that had two mouths. Perhaps, they hypothesized, this was a Frankenstein creation of two jellies that had spontaneously fused as one.  &�Բ�����;

Systematic tests confirmed their suspicions. Almost every time researchers spliced and combined tissue samples from two different jellies, a newly fused ctenophore emerged a few hours later, each specimen rearranging its biology to accommodate that of the other.  &�Բ�����;

It was more than a patchwork mosaic of tissues and cells, superficially cut and pasted; it was a complete reorganization.  &�Բ�����;

For example, researchers watched the two digestive systems merge into one functioning tract: Food sent through one mouth seamlessly traveled to the other’s gut. The two jellies also moved as one, synchronizing their contractions to coordinate a startle response.  &�Բ�����;

Based on these behaviors, it’s possible that the nervous systems integrated in the fused ctenophores – a feat “unheard of,” Arenas Sabogal said. If true, “it could have huge implications for regeneration, compatibility of tissues, and cell recognition systems.” &�Բ�����;

A “weird” nervous system  &�Բ�����;

Scientists don’t know much about the ctenophore nervous system, but “the more we investigate, the weirder it gets,” Arenas Sabogal said.  &�Բ�����;

In vertebrates, individual neurons are arranged in a network buzzing with information. The neurons communicate sequentially, releasing a chain of chemical and electrical signals from one to the next throughout the neural circuit.  &�Բ�����;

Comb jellies, however, assemble their machinery differently. These creatures develop individual neurons as expected, but later, those neurons fuse and mesh together, forming a net of cells.  &�Բ�����;

This summer, Arenas Sabogal is peering into the ctenophores’ puzzling physiology and running studies to determine how the nervous system transforms sensations into behavior. “Because they’re so different, there’s a possibility that they’re doing completely new stuff,” he said. 

 A mechanical sense &�Բ�����;

To ctenophores, the world is rich with sensations. They detect mechanical stimuli, perceiving the environment through changes in water pressure, gravity, and balance. But how does the animal detect these mechanical cues – or rather, how do their mechanical senses work?  &�Բ�����;

Molecular data suggest that one type of gene, piezo, may be connected to mechanosensation in ctenophores. &�Բ�����;

Piezo genes are mechanical receptors that encode a type of protein known as an ion channel. These help convert mechanical stimuli into cellular signals – a conversion that reveals useful information about the environment to the animal.  &�Բ�����;

Since showing piezo channels are present in ctenophores, Arenas Sabogal has measured their activity in some tissues sensitive to mechanical stimuli. He also investigated them in cells called balancers, which are part of a gravity-detecting complex and give the animal a sense of up and down.  &�Բ�����;

Piezo’s presence throughout the organism gave Arenas Sabogal “a good hunch that [the piezo channel] was going to be the mechanosensor,” so he developed several experiments to test how these ion channels work in ctenophores. Early results suggest that the ctenophore ion channels are incredibly conserved, persisting through 750 million years of evolution.  &�Բ�����;

Intelligent design &�Բ�����;

Scientists first sequenced the ctenophore genome a, which led to striking discoveries about its nervous system. Since then, it’s largely accepted that ctenophores are the ancestral organism, evolving earlier than either sponges or cnidarians (jellyfish). This implies one of two scenarios about its nervous system, Arenas Sabogal said.  &�Բ�����;

The first suggests that the nervous system traveled a fragmented evolutionary path, being lost in sponges and popping up again in cnidarians before continuing.  &�Բ�����;

The second proposes that the ctenophore nervous system evolved independently from cnidarians. In this scenario, ctenophores evolved an entirely unique way of perceiving and acting in the world, carving their own path to complex behavior.