In a drop of seawater, scientists found a tiny creature that challenges what we thought we knew about a whole group of microbes. This organism has a whip-like tail called a flagellum. Until now, no member of its family was known to carry a flagellum all the time.
Researchers successfully grew this flagellated protist from seawater samples. Under the microscope, it revealed a shape and internal layout unlike any other known flagellate. DNA tests showed it belongs to Endomyxa, a subgroup of rhizarians. Based on these clues, the team named it Viscidocauda repens.
Endomyxa includes many kinds of protists. Some live freely as amoebae in the sea. Others are parasites that infect animals, plants, and algae. Free-living flagellates had never been seen in this group before.
“Unlike the rhizarian subphylum Filosa, free-living flagellates have not previously been reported in Endomyxa,” a report notes.
The new genus shakes up this assumption. It means the common ancestor of Endomyxa might have had a flagellum. This insight opens a window into the early evolution of these single-celled life forms.
The discovery process began with simple cell cultures. Scientists took seawater and watched what grew. Few expected to see a creature waving a long tail. Detailed observations revealed its unique body plan. Inside, no other flagellates looked quite the same.
Molecular phylogenetic analysis placed V. repens at a basal position within Endomyxa. This means it branched off early from other members. It links the shape seen under the microscope with its genetic roots.
Source material explains that Endomyxan protists usually lack flagella or use them only at certain stages. In other words, finding a form that keeps its flagellum all the time was a surprise. Environmental DNA surveys had hinted at hidden diversity in Endomyxa, but no one had seen a living example like this.
The team also integrated insights from ultrastructural observations. They used electron microscopy to map internal parts. These scans confirmed that the flagellum sat where no one expected. The cell’s interior had features matching both free-living amoebae and parasitic kinds. This mix hints at how ancient protists might have diversified into many lifestyles—some free and waving tails, others hiding inside hosts.
From a practical angle, Viscidocauda repens helps fill a big gap in our map of life’s family tree. It shows that the evolutionary path of Endomyxa included forms that moved using a whip-like tail. Today, we know Endomyxa splits into groups like Gromiidea (marine amoebae), Vampyrellida (amoebae that feed on algae and fungi), Phytomyxea (plant parasites causing diseases like clubroot), and Ascetosporea (parasites of marine invertebrates). But none had a permanent flagellum, until now.
This finding also suggests that traits thought lost or absent might still appear in unexpected corners. The persistent flagellum in V. repens could mean that other branches of Endomyxa once had similar structures. Researchers hope to explore this idea by looking for more deep-branching relatives.
The study offers a reminder that even well-studied groups can hold surprises. Tiny drifting cells in the ocean might tell us big stories about how life evolved on Earth. With tools like DNA sequencing and high-resolution imaging, scientists are rewriting the textbooks bit by bit.
Researchers published the details of Viscidocauda repens in a recent issue of a peer-reviewed journal. Their work combines molecular data and detailed cell images. Together, these clues paint a picture of a lineage that straddles ancient and modern traits. By studying this new genus, we gain fresh clues about how single-celled life forms diversified into the many shapes we see today.
The study has been published in Protist.
