Using observational and chemical analysis, the scientists "confirmed that a high percentage of eggs were fertilized with sperm captured from the water. Sperm capture occurred in 100 percent of isolated individuals and, remarkably, even in 24 percent of individuals that had an adjacent partner."
Barnacle sex then involves some individuals shooting sperm from their penises, while others capture that sperm for egg fertilization. For humans, it would sort of be like trying to get pregnant by hugging in a hot tub with other potential mates present, but without actually having sex.
Barazandeh and team write that "these observations overturn over a century of beliefs about what barnacles can, or cannot, do in terms of sperm transfer" and "raise interesting questions about the capacity for sperm capture in other species."
Recalling barnacles stuck on boats, remember that these animals live by gluing themselves to surfaces. That in itself would seem to pose major limitations for baby making. But clearly barnacles, or at least this particular species, have overcome the challenges.
Top image: Goose barnacles cling to rocks washed by strong currents. Credit: Stuart Westmorland/Corbis.