Found unexpectedly in a lab culture, this protist doesn’t just resemble a tiny sun—it could also shine a light on the ancient origins of complex life.
The microorganism, which now defines its own genus, species, and phylum, offers rare insight into how early eukaryotic life may have formed. Its structure and genetic markers reveal traces of mitochondrial development, potentially challenging long-held views of cellular evolution.
The discovery was made by biologist Matthew Brown of Mississippi State University, who found the organism while studying anaerobic marine protozoans. Genetic analysis later confirmed that Solarion arienae not only belongs to a new group of eukaryotes—now classified as the supergroup Disparia—but also retains remnants of ancient metabolic systems that trace back billions of years.
A New Shape for Ancient Life
What sets Solarion arienae apart is its striking physical appearance. In its most common form, the microbe displays long appendages ending in orbs, giving it the silhouette of a cartoon sun or a mid-century chandelier. These structures, known as extrusomes, are used to capture bacterial prey. At the tips of each extrusome is a kinetocyst—hollow, piercing bodies that inject filaments into captured bacteria.
Only one other protist, Meteora sporadica, shares a similar structure. The main difference lies in the number of orbs per appendage: Solarion has one, while Meteora has several. The resemblance is so close that the two are now grouped in a newly established phylum named Caelestes. Inside the cell, the organism also displays a unique internal structure. Unlike most eukaryotes, which have two centrioles to help organize their cytoskeletons, Solarion contains just one that floats freely in the cytoplasm.
Surviving Pathways From a Distant Past
According to Brown, genetic tests showed that Solarion arienae carries fragments of ancient mitochondrial pathways that could date back to the earliest stages of eukaryotic life. These remnants include rare mitochondrial genes that are now typically found only in the cell nucleus of modern eukaryotes. One pathway in particular, known as SecA, drew the attention of Brown’s team.
This pathway usually works alongside SecYEG, a channel that helps move proteins within the cell. Yet, in Solarion, SecYEG is absent. Strangely, SecA is found inside the mitochondria instead of the cytoplasm or cell membrane, hinting that it may function differently or has been repurposed from ancient cellular machinery.
The findings were reported in a study published in Nature, where Brown noted that these features “shed light on the complexity of ancient eukaryotic life.” The presence of such traits in a modern organism suggests that parts of cellular evolution believed to be long gone may still be alive in hidden or rare species.
A Lifeform That Shifts Its Own Shape
While the organism’s sun-like form is its most recognizable, Solarion arienae undergoes a second phase in its life cycle. In this form, the appendages disappear, and the cell elongates, growing a flagellum that allows it to swim.
Unexpectedly, some of these elongated forms later revert to their previous sun-shaped state. According to Popular Mechanics, this back-and-forth transformation is rare among known protists and remains poorly understood.
Brown’s team discovered the organism while studying marine protozoans in low-oxygen environments. The fact that Solarion remained unnoticed until now raises questions about its preferred habitat. Researchers believe it may exist in very specific ecological niches or could be more widespread but overlooked due to its elusive behavior.