Ctenophores: Wonders of Biology
Recorded: Sept. 19, 2026, 7:09 a.m.
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Ctenophores Aren’t Just Beautiful. They’re Biological Wonders. | Quanta Magazine
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Comment Comments Save Article Read Later image gallery By Marlowe Starling September 16, 2026 Comb jellies are helping answer fundamental questions in biology, from how the earliest nervous systems evolved to how bioluminescence works. Comment Save Article Read Later space image gallery By Marlowe Starling September 16, 2026 Comb jellies are helping answer fundamental questions in biology, from how the earliest nervous systems evolved to how bioluminescence works. Comment Save Article Read Later Your browser does not support the video tag. The ribbonlike Cestum veneris, or Venus’ girdle, is one of the largest ctenophore species and grows up to 1.5 meters in length. Alexander Semenov/Aquatilis Expedition Your browser does not support the video tag. The ribbonlike Cestum veneris, or Venus’ girdle, is one of the largest ctenophore species and grows up to 1.5 meters in length. Alexander Semenov/Aquatilis Expedition
By Marlowe Starling September 16, 2026 View PDF/Print Mode animals. biology evolution evolutionary biology image gallery marine biology oceans All topics Around 700 million years ago, a group of organisms resembling little more than glowing, gelatinous blobs split off from the rest of the animals, forming possibly the earliest branching animal lineage. Nearly 200 species of ctenophores, commonly known as comb jellies (but unrelated to jellyfish), live today in environments ranging from the cold depths of the sea to warm coastal surface waters. Their magic isn’t just in their persistence or iridescence; it’s in their DNA. Share this article Copied! Copy link Ycombinator
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How the phylogenetic tree looks under the Ctenophora-sister hypothesis. Kristina Armitage/Quanta Magazine What makes this all the more surprising is that sponges lack muscles and neurons, while ctenophores have muscles and exhibit evidence of a simple nervous system. “If you think about the earliest branching animal lineage, you would expect less complexity,” Burkhardt said. “That changes a lot of the assumptions [about] how the very first animal may have looked.”
Comb jellies are ancient marine predators whose hairlike extensions known as cilia refract light as they swim, giving them an iridescent shimmer. They are the largest animals known to use cilia for movement, and use sticky cells called colloblasts to catch prey as they move through water.
Using volume electron microscopy, Burkhardt’s lab identified 17 unique cell types in Mnemiopsis leidyi — 11 of which were previously unknown — in an all-important structure called the aboral organ (center). Together, these cells help ctenophores sense light, pressure, and gravity, and the aboral organ is tightly integrated with a continuous network of fused neurons that forms the nervous system. “Having more neurons condensed at a certain place, that’s one theory [for] how the very first brains evolved,” Burkhardt said. The research was published in March 2026 in Science Advances. Alexandre Jan, Michael Sars Centre/University of Bergen
Nervous systems are typically defined as networks of neurons that communicate across synapses. But Burkhardt’s lab found something unique in ctenophores: Beneath the animal’s outer surface is a nerve net (pink mesh in this 3D reconstruction) whose neurons are connected by continuous cytoplasm — but with no synapses between them. “I don’t think any other animal has a nervous system like that,” Burkhardt said. Because ctenophores are one of the earliest branches of the animal family tree, the finding indicates that evolution may have crafted nervous systems twice: in ctenophores, and separately in jellyfish and all other animals. Pawel Burkhardt
Genome regulation is fundamental to determining when and where genes are turned on and off. But over long stretches of the genome, this process becomes more complicated, requiring DNA and proteins to physically fold into loops. Researchers think this was critical to enabling multicellular organisms to develop specialized cells without needing to evolve new genes. “These are key for cell-type specialization and building complex tissues,” said Arnau Sebé-Pedrós, an evolutionary biologist who studies genome regulation at the Center for Genomic Regulation in Barcelona. The ctenophore M. leidyi (pictured) has more than 4,000 loops in its genome of just 100 million base pairs (compared to 3 billion in the human genome), which suggests that looped DNA may have evolved 150 million years earlier than scientists thought. Joan J. Soto-Angel
Many species of marine life can produce their own light through bioluminescence. As one of the most distant relatives of other glowing multicellular organisms, ctenophores harbor clues in their genomes that point to how and why this evolved. Haddock’s team found that a few non-glowing ctenophore species lack genes that they suspect help synthesize a light-emitting chemical called coelenterazine. Subsequent research identified the full-length gene in bioluminescent ctenophores. “It’s the most abundant, widespread light-emitting molecule in the ocean,” Haddock said; it appears in copepods, shrimp, squid, mollusks, and more. “It is hard to explain how these things crop up independently across the tree of life,” Haddock said. “They’re maybe co-opting some kind of precursor gene that they [all] have, and then they’re modifying it to use it for a different purpose.” S. Haddock/MBARI/The Bioluminescence Web Page
When a tank of M. leidyi comb jellies in a lab shrank from 10 adults to nine adults and one larva over the course of a month, scientists cocked their heads in confusion. In 2024, ctenophores became the third group of animals known to have the Benjamin Button–like ability to reverse its development, joining the ranks of the “immortal jellyfish,” Turritopsis dohrnii, and a tapeworm, Echinococcus granulosus. The reverse development was triggered by prolonged starvation and injury. “They’re highly plastic, so they can live without food for really long periods,” Burkhardt said. “They can grow, they can shrink, and that tells you a lot about how the very first animals potentially also had that flexibility.”
Lipids are cone-shaped molecules that make up all cell membranes. Unlike most lipids, a special type called the plasmalogen only has one oxygen molecule instead of the usual two. Human brains have them, and so do deep-sea comb jellies. They flex in a way that makes it possible for the ctenophores to withstand extreme hydrostatic pressure. When the ctenophore Bathocyroe aff. fosteri was brought to the surface and released from that pressure (left), the plasmalogens expanded (center), cell membranes split apart (right), and the comb jelly disintegrated. “We went into this asking a very fundamental question about life in the deep sea,” Budin said, “but it involved a biomolecule that’s also very important in our bodies [and] in human health.” Fewer plasmalogens in human brains can be associated with neurogenerative diseases such as dementia, Budin said. These lipids may help cell membranes fuse and break fast enough for neurons to fire. Jacob Winnikoff
Two of the comb jelly species studied under pressure by Budin and colleagues show the animals’ remarkable variety and complexity. On the left is the deep-sea lobate comb jelly Bathocyroe aff. fosteri. “Bathocyroe” means “master of the deep,” and the species is found at depths ranging from 200 to more than 3,000 meters. The red pigmentation in the animal’s stomach is thought to block light emitted when it engulfs bioluminescent organisms, so its prey doesn’t give away its location to other predators. The shallow-water comb jelly Leucothea pulchra (right) is named after the Greek goddess of sea-foam. This species is rarely found deeper than 20 meters. The orange knobs are prehensile, sticky, and used for prey capture. Jacob Winnikoff
During embryonic development, cells arrange themselves into distinct morphologies due to a blastopore: an indentation that ultimately becomes the anus or mouth (central area pointing upward in this image of M. leidyi). The same developmental process for embryos in ctenophores is also found in bilaterians, the large group of animals that share our bilateral symmetry. This indicates that the blastopore organizer — which turns a mere ball of cells into a complex, multicellular embryo — is conserved across species. “Understanding where the organizer came from tells us which parts of our development are ancient and robust, and which are recent inventions,” said Andreas Hejnol, an evolutionary biologist at Friedrich Schiller University Jena in Germany. Human embryos use the same signaling pathways that Hejnol and his colleagues found in ctenophores. Lisa-Marie Barf
C. veneris uses cilia and muscular undulation to glide through the water column, preying on copepods and different types of larvae. The center of its long body houses its “flight control center,” which contains its stomach, major nerve networks, and primary sensory organs. It protects its vital organs from harm by curling its long body around itself. Alexander Semenov/Aquatilis Expedition
By Marlowe Starling September 16, 2026 View PDF/Print Mode animals. biology evolution evolutionary biology image gallery marine biology oceans All topics Share this article Copied! Copy link Ycombinator
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Ctenophores, or comb jellies, represent biological wonders that contribute significantly to understanding fundamental questions in biology, ranging from the evolution of early nervous systems to the mechanism of bioluminescence. Nearly two hundred species of ctenophores inhabit diverse marine environments, and studying them provides insights into adaptation, evolutionary pathways, and the physical, chemical, and biological principles governing life itself. The phylogenetic placement of ctenophores challenges traditional views, with recent evidence suggesting they may represent the sister group to sponges rather than being the most distant branch of the animal kingdom. This reassessment of evolutionary history is driven by comparative studies across varied environments, allowing researchers to investigate adaptations such as light sensing genes and responses to high pressure. Evolutionary biologists, such as Pawel Burkhardt, find ctenophores exciting subjects because they hold clues about the origins and evolution of neurons and nervous systems. The structure and organization of ctenophore biology reveal novel aspects of animal evolution. Research utilizing volume electron microscopy has revealed complex cellular organization, such as the aboral organ in species like Mnemiopsis leidyi, which integrates sensory input from light, pressure, and gravity via a network of fused neurons that forms the nervous system. This structure suggests a theory for how the earliest brains might have evolved through the condensation of neurons. Furthermore, the nervous system in ctenophores is unique; it consists of a nerve net where neurons connect via continuous cytoplasm without traditional synapses, suggesting that evolution may have developed nervous systems multiple times across the animal lineage. Genome regulation in ctenophores also offers deep evolutionary insights. The presence of highly looped DNA, with species like M. leidyi exhibiting thousands of loops in a relatively small genome, suggests that mechanisms for genome folding may have evolved much earlier than previously estimated. This looping is proposed to be critical for allowing multicellular organisms to achieve cell-type specialization and build complex tissues. The study of ctenophores also sheds light on the molecular basis of other biological phenomena. In relation to bioluminescence, research has explored genomic clues that suggest ctenophores co-opted precursor genes to synthesize light-emitting molecules, hinting at a shared evolutionary mechanism across multiple disparate organisms. These organisms display remarkable plasticity, exemplified by the ability of some ctenophores to reverse their developmental stages from adult to larval forms in response to starvation or injury, indicating that flexibility in development may be an ancient trait in the earliest animals. Furthermore, the structural integrity of ctenophore cells is maintained by specialized lipids, such as plasmalogens, which allow them to withstand extreme hydrostatic pressure in the deep sea. The behavior of these lipids under pressure has implications not only for deep-sea life but also for cell membrane fusion and signaling pathways relevant to human health. Morphologically, ctenophores exhibit diverse adaptations related to their habitats. Species inhabiting the deep sea, such as Bathocyroe aff. fosteri, display red pigmentation in their stomachs, hypothesized to block light emitted by prey. Other species utilize cilia for locomotion and possess specialized structures that integrate sensory functions with their nervous system. Understanding the conserved developmental processes, such as the role of the blastopore organizer, across ctenophores and bilaterians underscores the antiquity of key developmental mechanisms in animal evolution. Collectively, the investigation into comb jellies demonstrates that studying seemingly unusual organisms can reveal universal physical, chemical, and biological principles applicable to understanding the entire spectrum of life. |