The worm that emerged from the depths of the Orinoco

The biologist Carlos Lasso during a collection of fauna and the marine worm that was discovered in the Orinoco River. Alessio Romeo-La Venta

The biologist Carlos A. Lasso hesitated a lot when observing those worms through the magnifying glass.

"Taking into account the ecosystem from which they were extracted, it was very strange that they were polychaetes," he says, referring to this class of invertebrates.

During the confinement due to the covid-19 pandemic, he sent the sample to an expert, but he did so “with great caution, confessing that, perhaps, it was only the root of a plant, a vegetable stem, or another organism that did not know”.

A few months later, the specialist Mario Londoño, from the Colombian University of Antioquia, confirmed his discovery: a freshwater worm in the depths of the Orinoco, the river that crosses the border territory between Venezuela and Colombia and the largest after those that cross the Amazon and the Congo.

“The remarkable thing about the research is that this fauna is generally marine.

Freshwater species are usually found in estuaries near the coast, never that far away.

I found these worms in deep and rapid waters 1,000 km from it”, explains the biologist.

Belonging to the group of annelids, such as earthworms or leeches, polychaetes are the most numerous of the phylum and are found in all geographical areas of the world, many of their species remaining hidden in the sediments of the seabed.

Another of the curiosities that caught the biologist's attention “is that these were attached to sponges and bivalve shells”, part of the fauna with which he investigates.

That, according to his hypothesis, "would point to some symbiotic or mutualistic relationship with this type of animal."

For more than 12 years, Lasso, a native of Madrid who has been on the Latin American continent for almost four decades, has been conducting surveys to study the biodiversity of aquatic fauna and hydrobiological resources at the mouth of the Orinoco, at the foot of the Colombian municipality of Puerto Carreño, capital from the department of Vichada.

"We take advantage of the dry season, from January to April, when the river level does not exceed 10 meters, to make the dives," explains the Humboldt Institute researcher.

This center based in Bogotá is located an hour and a half by plane from the whereabouts where Lasso has found the new species of worm, currently in the process of taxological description.

According to Londoño, to whom Lasso first sent some photographs taken with his cell phone and then one of the samples he collected, the specimen hitherto unknown in the scientific community would belong to the genus Manayunkia, of the Sabellidae family.

It is "a vector of parasites in fish such as salmon, which could be important for the aquaculture industry," continues the biologist.

Image of the worm found in the Orinoco River. Alessio Romeo-La Venta

However, in addition to its possible importance for the said sector, the relevance of the polychaete lies in the fact that "it could constitute one more proof of the transgressions and marine regressions suffered by the Amazon and Orinoco regions," the researcher points out.

In search of cryptic species

According to some scientific interpretations, a theory still in controversy in the academic field, the geological history of some hydrographic regions of Latin America was crossed by the existence of an extensive and shallow sea that covered the Amazon and current Orinoco for millions of years. .

According to a study published in 2017 in the journal

, the Caribbean Sea bathed the freshwater territories that today cross Venezuela and Colombia on two different occasions during the Miocene, which, according to that thesis, would explain the evolution and distribution of life product of extreme geological changes.

“Like the Amazon, the Orinoco, which reaches up to 100 meters deep, was subject to changes in its ecosystem, which caused some species to become extinct and others to survive by adapting to the new conditions.

There is already evidence of sponges, jellyfish or even freshwater rays whose ancestors of marine origin were found in these rivers”, says the biologist.

"Another interesting piece of information about these polychaetes is that they were able to co-evolve with the sponges and bivalves to which they are associated, a very exceptional case in nature," continues Lasso.

Biologist Carlos Lasso with a collaborator.

Alessio Romeo-La Venta

With more than 1,650 fish described so far, one of the characteristics of the Orinoco ecosystem is its amazing biodiversity.

According to the man from Madrid, “every time an exploration is carried out in this region, something new is found.

Finding unknown organisms in the tropical environments of South America is relatively common.

The most interesting thing for me is finding cryptic species.”

That is, those that, being different, have been classified as one.

To find this type of fauna, which often remains hidden in unexpected places, Lasso goes beyond standard collection methods.

"I carry out nocturnal sampling at great depths with zooplankton trawls, with light traps and underwater dives," explains the zoologist, accustomed to inspecting the strangest habitats,

to examine in detail stone by stone, to put the magnifying glass inside trunks and roots.

“And at the institute, together with the Universidad de Los Andes, we carry out studies of environmental DNA in deep waters, known as

”.

This new technique, which studies the genetic material freely roaming in ocean ecosystems and in many aquifer systems, is a non-invasive method to assess the composition, distribution and census of organisms in various habitats.

"However, I found these new polychaetes after collecting rocks with the aim of looking for sponges and bivalves," says the zoologist who, together with other specialists from the University of Antioquia, has formed a group to continue advancing in the knowledge of the new worm.

“It is teamwork and each one takes advantage of the strength and academic knowledge available to complete all possible information about the newly discovered species.

I am in charge of collecting the ecological information, the other part is focusing more on the genetic aspect.

One of the objectives of this study is to carry out molecular analyses”, announces the specialist.

"A very fortuitous finding, like many advances in science, they are the product of chance," acknowledges Lasso,

Subscribe here

to the EL PAÍS América

and receive all the key information on current affairs in the region