Mysterious Parasitic Larva: Scientists Unravel Its Secrets After Nearly Two Centuries of Fascination

A kind of parasites intrigues scientists

Each new discovery on the marine environment reminds us a little more than we know almost nothing about it, or how to explain it. One of the most speaking examples is that of facetotecta (Hansenocaris).

However, a recent study published on July 21, 2025 in the journal Current Biology could provide new details on the facetotecta. An international team has collected more than 3000 larvae belonging to this species and who live on the surface of the Pacific Ocean near Japan. This allowed them to build the first family tree of this species.

They are linked to classic barns … but not those parasitic

After carrying out genetic tests, the researchers discovered thanks to their family tree based on Crustaceans RNA protein models, which the facetotecta were related to the barns (Semibalanus sp). These small marine crustaceans are found in the surfaces of boats, rocks or on the shells of turtles and whales.

However, the research team was surprised by the type of barns to which the facetotecta were related. Indeed, there are two kinds of barnes: the first is that cited above, Semibalanus sp, and the second called Rhizocephala represented by parasitic barns.

“We were finally able to confirm, in the field of megadowed science, that they are in fact related to the barnes, but that they are not closely related to any other parasitic barne”, explains James Bernot, environmentalist of the University of Connecticut and one of the authors of the study.

Similarities and differences with parasitic strips

Although these two groups seem to be distant from a kinship point of view, they turn out that they still have similarities. Indeed, a study published in 2008 in the journal BMC Biology, had shown that the juvenile stadium of facetotecta represents a remarkable convergence with that observed in parasitic barns.

However, researchers have discovered that these parasites infest their hosts in adulthood, and live freely when they are young. Which usually does not happen in other parasitic species, such as the Rhizocephala.

Normally, parasites infest their host when they are at the larval stage, and develop until adulthood in their bodies. Parasitism in the barnes is also very special.

“They deceive their hosts by making them believe that they are pregnant so that they begin to take care of this mass which develops outside their body, but this mass is part of the barne and does not really constitute the eggs of the host, and even if they infect a male crab, it is feminized and begins to behave like a pregnant crab female”, explained the environmentalist, in remarks reported by Science.

If the future of adults Facetotecta remains a mystery, its phylogenetic position is a great advance for specialists and their understanding of the evolution of parasitism in this group of unusual crustaceans.

Source: Sciencealerlet