520-Million-Year-Old 'Sea Monster' With 18 Tentacles Could Be Comb Jellies' Ancestor

A 520-million-year-old fossil of a sea creature with 18 tentacles around its mouth was found in China. The fossil could help solve a modern-day mystery about the origins of a gelatinous carnivore called a comb jelly, a study published in the scientific journal Current Biology revealed last week.

According to the study, the "sea monster," which scientists dubbed Daihua sanqiong, shares a number of anatomical characteristics with the modern comb jelly.

"When I first saw the fossil, I immediately noticed some features I had seen in comb jellies,” Jakob Vinther, a molecular palaeobiologist, said in a statement. “You could see these repeated dark stains along each tentacle that resembles how comb jelly combs fossilize. The fossil also preserves rows of cilia, which can be seen because they are huge. Across the Tree of Life, such large ciliary structures are only found in comb jellies.”

Comb jellies use bands of iridescent, rainbow-colored comb rows along their body to swim. These rows are composed of densely packed cellular protrusions, known as cilia. According to the study, these combs may have evolved from the ancient tentacles seen in the Daihua.

"To make a long story short, we were able to reconstruct the whole [early] lineage of comb jellies," by doing anatomical comparisons, Vinther said, adding that along with the similarities with comb jellies, the discovery of the ancient sea monster was a big deal as it may have been among the first animals to evolve on Earth.

However, Casey Dunn, a professor of ecology and evolutionary biology at Yale University who was not involved with the study, questioned the results. In an interview with Live Science, he said he was "highly skeptical of the conclusions they draw."

The 18 tentacles of the Daihua contained "fine feather-like branches with rows of large ciliary hairs," which were used to help the creature catch prey, the statement added. However, Daihua isn't the only ancient creature to have so many arms. Another ancient creature called Xianguangia had 18 tentacles, along with the tulip-like sea creatures Dinomischus — which lived 508 million years ago and had an organic skeleton — and Siphusauctum.

“We also realized that a fossil, Xianguangia, that we always thought was a sea anemone is actually part of the comb jelly branch,” co-author Cong Peiyun, said in the statement.

In the study, the researchers demonstrate how the comb jellies evolved, describing the organic skeleton it had during the Cambrian period — earliest time division of the Paleozoic Era, extending from 541 million to 485.4 million years ago.

"These are exciting animals no matter how they're related to each other," Dunn said. "Even though I'm skeptical that tentacles and comb rows are homologous [evolutionarily related], I think that as we describe more diversity from these deposits, certainly we're going to learn a lot more about animal evolution."