Researchers have identified 518-million-year-old fossils of a tiny sea creature, Yujingia glutenotunica, in southwestern China. The discovery challenges long-standing evolutionary models, suggesting that the common ancestor of starfish and their relatives fed using tentacles rather than filtering particles through a throat-based system as previously believed.
Anatomy of the Yujingia Discovery
The specimens measure between 8 and 22 millimeters in length. The fossils were unearthed in the Maotianshan Shales of Yunnan Province, a site renowned for preserving soft-bodied organisms from the Cambrian explosion. Unlike many specimens from this era that consist only of mineralized skeletons, these fossils retain detailed impressions of internal organs, including the gut and a surrounding gelatinous membrane.
Lead author Kaiyue He of Northwest University noted that the creature’s shape resembles a traditional Chinese ritual vase, known as a yujingping,
which inspired the name Yujingia. The species name, glutenotunica, reflects its soft, gelatinous appearance preserved in the rock.
Revising the Ancestral Worm Model
The discovery of Yujingia alters this perspective by providing physical evidence of a tentacle-based feeding system in a primitive relative. For decades, evolutionary biologists hypothesized that the last common ancestor of the Ambulacraria—the group containing both echinoderms like starfish and hemichordates like acorn worms—was a simple, burrowing worm that filtered food through its pharynx.
“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.”
Giovanni Mussini, Cambridge’s Department of Earth Sciences
The animal possessed two sets of appendages. One set featured feather-like arms for capturing organic particles, while a second set likely acted as an anchor to the seafloor. According to researchers, this specialized feeding apparatus suggests that complex structures evolved much earlier in the ambulacrarian lineage than previously recognized, predating the development of the hard skeletons seen in modern echinoderms.
Tracing Evolutionary Divergence
The results place Yujingia as a transitional form near the base of the ambulacrarian branch. The study, published in Current Biology, utilized Bayesian phylogenetic reconstruction to analyze 505 anatomical characteristics across 100 living and extinct species. This positioning helps explain the profound differences between the fivefold radial symmetry of starfish and the bilateral, elongated bodies of acorn worms.
Researchers suggest that ecological pressures were the primary catalyst for these divergent body plans. While chordates, the lineage leading to humans, became increasingly reliant on movement and brain development to secure food, the ancestors of starfish adopted a more sedentary, particle-feeding lifestyle.
“It tells us how ecology can drive different lineages onto very different evolutionary paths, and very different morphological specialisations. 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 specialised on this particle-feeding lifestyle.”
Giovanni Mussini, Cambridge’s Department of Earth Sciences
Unresolved Cambrian Questions
Despite the insights provided by the recovered specimens, several questions persist.
The research team included scientists from Northwest University, the University of Cambridge, the China University of Geosciences, and two German museums. The project received support from the Natural Environment Research Council (NERC) as part of UK Research and Innovation (UKRI).