Comb Jelly: World’s Most Primitive Animal?

by Dr. Elizabeth Mitchell on December 28, 2013


Science: Your Cousin Was a Comb Jelly

Move over sponges and yield your ancient throne to our sister the sea walnut.

Evolutionary scientists used to think that sponges gave animal evolution its kick up the evolutionary tree. Genomic and biological analysis of warty comb jelly—also known as a sea walnut—now demonstrates, researchers claim, that the comb jelly is the oldest living cousin of all animals, including of course human beings.


This is a comb jelly, also known as a sea walnut. It resembles a jellyfish but lacks stinging cells. Eight rows of linked cilia, resembling combs, propel about 200 species of these organisms through marine ecosystems all over the world. Because comb jellies have nerve and muscles cells, they seem more complex than sponges. However, evolutionary researchers believe the comb jelly’s genome shows that its kind is a more primitive ancestor of multicellular animals than sponges. Image: Stefan Siebert/Brown University in ScienceShot

At the Foot of the Animal Tree

Evolutionists trying to trace the lineage of all animals back to its base have long debated what sort of organism is the most primitive. The sponge—with its deceptively simple design—has long been a leading candidate. Contenders include other jellyfish-like animals and placozoans—a sort of flat ciliated multicellular marine algae-eater aptly nicknamed “a sticky hairy plate.” Now, Joseph Ryan and colleagues, reporting in Science that they have sequenced the genome of the first comb jelly—a species called Mnemiopsis leidyi—say they wish to re-write the way early animal evolution is supposed to have happened.  

The comb jelly is named for its eight rows of linked cilia that look like combs and propel it through the water. There are around 200 species of this marine creature. It looks like a jellyfish but lacks stinging cells. Comb jellies also, like sponges and jellyfish and placozoans, lack brains. Known as a sea walnut due to its shape and slow motion, the comb jelly is actually a fairly invasive species when inadvertently introduced into ecosystems lacking its ordinary competitors. In the 1980s a species of comb jelly wreaked havoc in the Black Sea by consuming so many anchovy fish eggs that the fishing industry has yet to fully recover.

Complex Primitivity

The comb jelly, it turns out, has some of the same complex nerve and muscle cell types as multicellular animals with bilateral symmetry. These nerve and muscle cells are diffusely arranged in a net, radially symmetrical around the comb jelly’s gravity-sensing organ. Sponges and placozoans seem simpler than comb jellies because they lack such nerve and muscle cells, and because they have simpler body plans.1 Nevertheless, Ryan and colleagues suggest that the sponge should be de-throned as the most basal ancestor of all animals and replaced with the comb jelly.

After comparing the comb jelly’s genome to those of the other contenders and more complex multicellular animals, Ryan’s group has concluded that the evolution of animals has not been merely a matter of evolving greater complexity. Instead, they believe that various branches of animals evolved certain complex cell types and then lost them, leaving only a ghost of the past in their genomes.

Ryan and colleagues explain:

Our phylogenetic analyses suggest that ctenophores [comb jellies] are the sister group to the rest of the extant animals. We find that the sets of neural components present in the genomes of Mnemiopsis and the sponge Amphimedon queenslandica are quite similar, suggesting that sponges have the necessary genetic machinery for a functioning nervous system but may have lost these cell types. We also find that, although Mnemiopsis has most of the genes coding for structural components of mesodermal cells, they lack many of the genes involved in bilaterian mesodermal specification and, therefore, may have independently evolved these cell types.

These results present a newly supported view of early animal evolution that accounts for major losses and/or gains of sophisticated cell types, including nerve and muscle cells. This evolutionary framework, along with the comprehensive genomic resources made available through this study, will yield myriad discoveries about our most distant animal relatives, many of which will shed light not only on the biology of these extant organisms but also on the evolutionary history of all animal species, including our own.2

But does the comb jelly deserve this new notoriety? Is either the sponge or the comb jelly a reasonable candidate for our oldest living cousin? Of course not. Evolutionists assume that all life evolved from less complex ancestors. This process, however, for all their certainty that evolution is the only explanation for the existence of life, has never been observed to happen.

Evolutionists have generally assumed that life evolved from the simple to the complex. Greater knowledge of biology in general and the genomes in particular has now demonstrated that even these somewhat simple organisms cannot be easily lined up from simplest to most complex. The evolution of complexity cannot be traced up the line. Of course, even if it could, the ability to line up a series of organisms in some sort of logical order does not demonstrate that any of those organisms were able to randomly acquire the genetic information to evolve into the next most complex kind of organism.

Tangled Web

Nothing about the genome of the comb jelly or any other candidate for most ancient ancestor indicates these animals are the ancestors of anything.
In any case, these organisms do not cooperate with the evolutionary scheme demanding increasing complexity. The candidates for the most basal little beastie on the tree of life are all more complex and diverse than originally suspected by those arguing over the occupant of the primitive throne. The only way to force these remarkably complex “simple” organisms into the pigeonholes evolutionists have prepared for them is to weave a story of gaining and losing information. Genes that bear some similarity to genes in other organisms are simply assumed to have a common ancestral source in the evolutionary saga, but this cannot be demonstrated.

Nothing about the genome of the comb jelly or the sponge or any of the other candidates for most ancient ancestor indicates these animals are the ancestors of anything or anybody. They simply are what they are. Since the changes needed to evolve from one kind of organism into another have never been observed, however, it would make more sense to abandon the evolutionary paradigm and consider evaluating the evidence in light of the only historical eyewitness record of our origins available—the history in the book of Genesis, God our Creator’s eyewitness account of our origins.

The Bible records that God created all kinds of living things about 6,000 years ago. Those living things reproduce after their kinds and vary only within their kinds. That is what we observe in biology. The latest study reveals something of the complexity of comb jellies and sponges. They are complex and simple in different ways. These sorts of organisms—like everything else on earth—were created by our Creator.

This is exactly what we would expect from a common Designer: many living things sharing common designs—genetic, cellular, anatomic, biochemical—many of which get used in somewhat different ways that allow for life in the same world. Comb jellies, sponges, jellyfish, and placozoans are great examples of common designs diversely displayed, examples of our Creator’s handiwork.

Further Reading:

And Don’t Miss . . .

  • This past week we covered two studies about cobras and pythons and what secrets these snakes’ genomes reveal, and then we considered what some beautifully preserved and quite modern-looking fig wasps were doing so deep in a quarry in Brazil.
  • This coming week, we close out 2013 with an overview of some amazing animals that made the news this year, and we’ll start out 2014 “fleshing out” a mini dinosaur mystery. And who knows what else will be in the News?

For More Information: Get Answers




  1. A. Rokas, “My Oldest Sister Is a Sea Walnut?” Science 342 (13 December 2013):1327–1329, doi: 10.1126/science.1248424.
  2. J. Ryan et al., “The Genome of the Ctenophore Mnemiopsis leidyi and Its Implications for Cell Type Evolution,” Science 342 (13 December 2013), doi:10.1126/science.1242592.

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