The comb jellies separated from other animal groups around 700 million years ago, according to recent findings. These studies suggest they might have been the first branch to diverge from the main line of animal evolution, even though they possess muscles and a rudimentary nervous system — features that run contrary to the idea that the earliest animals were more basic in form.
The Split That Changed Everything
Scientists long believed that sponges, known as porifera, were the first to branch off from the animal family tree — the sister group to all other animals. That view held for well over a century. However, evidence has accumulated over the past two decades suggesting that ctenophores came first instead. In 2023, following years of a “ping-pong game” between labs over which group was first, a landmark paper analyzing chromosome organization concluded that ctenophores, not sponges, are the sister group. This conclusion remains open to further investigation.
The discovery alters many long-held ideas about what the earliest animal might have resembled.
What Makes Them Surprising
What gives ctenophores their surprise is what they actually possess. Sponges lack both muscles and neurons. In contrast, ctenophores come equipped with muscles and show evidence of a simple nervous system.
“If you think about the earliest branching animal lineage, you would expect less complexity,” said Pawel Burkhardt, an evolutionary biologist at the University of Bergen who studies the origins and evolution of neurons and nervous systems. “That changes a lot of the assumptions [about] how the very first animal may have looked.”
Why Researchers Love Them
Having access to closely related species across such variable environments “lets you ask questions about how certain things evolved,” such as adaptation to high pressure or light-sensing genes, said Steven Haddock, a marine biologist who studies ctenophores at the Monterey Bay Aquarium Research Institute.
Burkhardt made the remark, according to “They’re very exciting to work with, and they’re also extremely beautiful organisms,”.
Reversing Development
Scientists have recorded certain creatures going back through their life cycle, from full-grown adults into earlier, more youthful forms. Other living things carry unusual kinds of fat that protect them against crushing force far below the ocean’s surface.
The traces they preserve point toward the development of increasingly intricate bodily forms.
The Case for Strange Life
Itay Budin, a biophysicist who studies cell membranes at the University of California, San Diego, makes a broader argument for studying odd life forms. “It’s really important to study organisms that might seem strange or weird because they can tell us a lot about the physical, chemical, and biological principles of life, which can then be applied to ourselves,” he said.
“We are as distantly related to a ctenophore as a ctenophore is to a jellyfish.”
What We Know Now
New findings keep coming to light. The chromosome organization study marked an important milestone, yet the matter remains unresolved.
The Beauty and the Wonder
Ctenophores aren’t just pretty. They’re biological wonders.
A Single Paper’s Data
| Group | Traits |
|---|---|
| Sponges (porifera) | Lack muscles and neurons |
| Ctenophores | Have muscles, simple nervous system |
Why This Matters
Evidence from comb jellies is changing how scientists understand the history of early animals. These findings point to a period when the first animals were far more complex than researchers previously assumed.
See the video the story is built around at Quantamagazine.
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