A creature preserved for 518 million years hints that the starfish family began with tentacles, challenging a long-standing picture of its earliest ancestor.
Fossils discovered in southwestern China suggest that an animal called Yujingia glutenotunica lived close to the evolutionary roots of ambulacrarians, the group that includes starfish, sea urchins, and acorn worms. Its anatomy challenges the longstanding idea that their common ancestor was a burrowing worm that filtered food through its throat and gill openings.
The international team, including researchers from the University of Cambridge and Northwest University in China, reported the findings in Current Biology. The discovery could help explain how related animals developed bodies as different as those of starfish, worms, and humans.
A Soft Body Preserved In Stone
Yujingia lived during the Cambrian explosion, when most major animal groups first appeared in the fossil record. Much of the evidence from this period comes from creatures with hard shells or skeletons. Soft bodies usually decayed before they could leave such detailed traces.
The Maotianshan Shales in China’s Yunnan Province offer a rare window into that otherwise missing history. Conditions there preserved the bodies, guts, and appendages of Yujingia, providing rare examples of early ambulacrarians without mineralized skeletons. The specimens measure 8 to 22 millimeters (about 0.31 to 0.87 inches) long.
The tweo sets of appendages reveal how the animals likely lived. Feather-like feeding tentacles gathered organic particles suspended in the water, while a second set likely held them temporarily against the seabed. Although they spent time attached to the bottom, they probably could move to some degree.
“The animal has an elongated, bottle-like form, with tentacles spreading above a rounded lower body,” said lead author Kaiyue He from Northwest University in China. “Its outline closely resembles the ritual vase, or yujingping, in traditional Chinese culture, which inspired the genus name Yujingia. All the specimens clearly preserve a pale, original membrane enclosing the visceral mass. Its soft, gelatinous appearance is the species’ most immediately recognizable feature and inspired the species name.”
Rethinking the Ancestor of Starfish
Ambulacraria, first classified in the 1880s, is one of the two major branches of deuterostome animals. It includes echinoderms (such as starfish) and hemichordates (such as acorn worms). Chordates, the other major branch, include humans. Reconstructing the ancestral ambulacrarian helps researchers understand how these lineages developed different bodies and ways of feeding.
“There has been a tendency to think of the last common ancestor of ambulacrarians as more closely resembling a worm living in its seafloor burrow, filtering food from the water,” said co-author Dr. Giovanni Mussini, from Cambridge’s Department of Earth Sciences. “This new fossil suggests instead that the common ancestor of the ambulacrarians might have actually fed with tentacles and may have been more like starfish and their relatives.”
“The fivefold radial symmetry of starfish and their relatives and the bilaterally symmetrical, worm-like bodies of acorn worms and their relatives has been a bit of a mystery until now,” said Mussini.
Tracing a Missing Evolutionary Link
To place Yujingia in the animal family tree, Mussini and He assembled a dataset of 505 anatomical characteristics across 100 living and extinct taxa. They used Bayesian phylogenetic reconstruction, a statistical approach that evaluates possible evolutionary relationships using shared features.
The results placed Yujingia closer to the last common ancestor of living ambulacrarians than previously described fossils. Rather than establishing it as the ancestor itself, the analysis identifies it as a particularly informative relative near that ancestral branch.
Its combination of traits connects early Cambrian animals with tentacles to the lineages that produced modern hemichordates and echinoderms. It also suggests that an elaborate feeding system evolved before echinoderms acquired their hard skeletons and other specialized features.
“How the major deuterostome groups diverged during the Cambrian explosion is one of the central questions in animal evolution,” said co-author Degan Shu, also from Northwest University. “Yujingia helps connect primitive, tentacle-bearing animals living on the seafloor with modern echinoderms and hemichordates. It offers a new way to understand the profound transition from bilateral symmetry to the fivefold radial body plan of echinoderms and adds an important fossil to a crucial gap in the early animal tree of life.”
How Feeding Could Shape Animal Bodies
The fossils also offer a way to connect anatomy with lifestyle. An animal that collects passing particles while attached to the seabed faces different demands from one that moves through its surroundings to find food. Over evolutionary time, those demands could favor very different structures.
“It tells us how ecology can drive different lineages onto very different evolutionary paths and very different morphological specializations,” said Mussini. “The chordates became reliant on movement for finding their food, so they streamlined their bodies and developed their brains, while members of the starfish lineage remained relatively anchored to the seafloor and specialized in this particle-feeding lifestyle.”
Reference: “Cambrian fossils illuminate the ambulacrarian common ancestor” by Kaiyue He, Giovanni Mussini, Jian Han, Mike Reich, Qiang Ou, Meirong Cheng and Degan Shu, 16 September 2026, Current Biology.
DOI: 10.1016/j.cub.2026.08.053
The research was supported in part by the Natural Environment Research Council (NERC), part of UK Research and Innovation (UKRI). Giovanni Mussini is a Fellow of Sidney Sussex College, Cambridge.
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