A strange worm emerges from one of South America’s longest rivers | Science & Tech

Biologist Carlos Lasso (wearing glasses) during a collecting expedition and the previously undiscovered worm he discovered in the Orinoco River.
Biologist Carlos Lasso (wearing glasses) during a collecting expedition and the previously undiscovered worm he discovered in the Orinoco River.Alessio Romeo La Venta

A few years ago, biologist Carlos A. Lasso did a double take when examining an odd-looking worm with a magnifying glass. He thought the object could possibly have been “the root of a plant, a stem of a vegetable, or some other unknown organism.”

During the Covid-19 pandemic, he sent the sample to an expert. A few months later, specialist Mario Londoño from the University of Antioquia in Medellín confirmed the discovery: it was a freshwater worm from the depths of the Orinoco, a 2,700-kilometer river that forms parts of the border between Venezuela and Colombia.

“Freshwater species are usually found near the coast. The remarkable thing is that I found these worms in deep and fast waters, more than 600 miles from the ocean,” explains Lasso.

Another thing that caught the biologist’s attention was that the worms “were attached to molluscs.” According to Lasso’s hypothesis, this would imply a relationship between the invertebrates.

For more than 12 years, Lasso – a Madrid native who has worked in Latin America for nearly four decades – has been conducting surveys to study the biodiversity of aquatic fauna and hydrobiological resources in the Orinoco estuary. He lives in the Colombian municipality of Puerto Carreño, capital of the department of Vichada.

“We use the dry season from January to April – when the river level does not exceed 9 meters – for the dives,” explains the researcher, who is part of the Humboldt Institute in Bogotá.

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Lasso and Londoño believe the specimen, previously unknown to the scientific community, belongs to the genus Manayunkiaof Sabellidae Family. It’s “a carrier of parasites in fish like salmon that could be important for the aquaculture industry,” says the biologist. He also believes that in addition to its ability to capture parasites, the worm could be evidence of “the transgressions and marine declines afflicting the Amazon and Orinoco regions.”

A microscopic image of a freshwater worm recently discovered in the Orinoco River.
A microscopic image of a freshwater worm recently discovered in the Orinoco River.Alessio Romeo La Venta

Some hotly debated scientific theories suggest that a vast and shallow sea may have covered large parts of South America – including the Amazon and the Orinoco Basin – for millions of years. According to a 2017 study published in the journal scientific advances, the Caribbean Sea twice bathed the freshwater areas that make up present-day Venezuela and Colombia during the Miocene, the first geologic epoch. This work would explain the evolution and distribution of fauna in the region.

“Like the Amazon, the Orinoco — which can reach depths of more than 300 feet — has been subject to changes in its ecosystem that have caused some species to become extinct and others to survive by adapting to the new conditions. This can already be seen in jellyfish or freshwater rays, whose ancestors were found in these rivers,” explains Lasso.

Biologist Carlos Lasso with a collaborator.
Biologist Carlos Lasso with a collaborator.Alessio Romeo La Venta

With more than 1,650 fish identified to date, one of the characteristics that sets the Orinoco ecosystem apart is its amazing biodiversity. “Every time an exploration is carried out in this region, something new is found,” says the Spanish biologist. Finding unknown organisms in the tropical environments of South America is relatively common.”

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To find new fauna, often hidden in unexpected places, Lasso goes beyond the usual gathering methods. “I do deep night sampling with zooplankton trawls, light traps and underwater dives,” he says. Lasso is used to patiently inspecting the strangest habitats, often sticking his magnifying glass into trunks and roots.

“In the [Humboldt Institute], together with the University of Los Andes we are doing deep-sea studies of environmental DNA, known as metabarcoding,” he explains. This new technique, which studies genetic material that roams freely in marine ecosystems and in many aquifer systems, is a non-invasive method to assess the composition and distribution of organisms in different habitats.

Lasso and several specialists from the University of Antioquia have formed a working group to further gather knowledge about the new worm. “I’m in charge of gathering ecological information…the other group focuses more on the genetic aspects [of the worm]’ says the biologist.

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