Balanus trigonus, the triangle barnacle, is a species of barnacle in the family Balanidae. They are steep-sided, conical creatures, have six shell plates and are dark pink in colour. Originally found only in the Indo-Pacific and along the eastern Pacific coast, they were likely introduced to the Atlantic Ocean in the 19th century through human activity and now has a global distribution. Usually living on subtidal rocks and shells, they are also foulers of ships and dock infrastructure, and, in areas where they are invasive, may compete with native species for living room. The species was first described in the genus Balanus by Charles Darwin. It has since had its mitochondrial genome sequenced twice, with slightly differing results, leaving its phylogenetic position unsolved.

Taxonomy: Balanus trigonus was first scientifically described in 1854 by Charles Darwin, with its current name. B. trigonus is commonly known as the "triangle barnacle". Darwin noted the species´ wide distribution and found that young Balanus trigonus appear quite similar to Balanus tintannabulum; he described the species as being found in association with B. tintannabulum as well as with Balanus psittacus, B. improvisus, B. amphritite, and Elminius modestus. He thought the new species most closely related to Balanus spongicola.

Genetics: The mitochondrial genome of the triangle barnacle has been completely sequenced – twice. The mitochondrial genome is the DNA found in the mitochondria and making up just a part of the organism´s entire genome; it can be used to trace maternal lines of descent. A 2021 study from South Korea found that triangle barnacles´ mitochondrial DNA comprises base pairs and 37 genes with an order and traits similar to other Balanid species. The mitochondrial genome comprises 22 transfer RNA genes, two ribosomal RNA genes, and 13 protein-coding genes – for comparison, the human genome has about 20,000 of the latter. However, a study published earlier the same year based on Chinese specimens published similar results, except for a larger genome, with base pairs. The goal of both studies was to better understand Balanus trigonus´ phylogenetic position based on the mitogenomes, though they yielded different results. The Korean study, considering the mitogenomes of 28 barnacles, placed B. trigonus closest to a clade comprising Fistulobalanus albicostatus and Amphibalanus amphitrite. The Chinese study, however, considered 30 barnacle species and concluded that B. trigonus paired with Acasta sulcata. F. albiostatus and A. amphitrite were included in the study, but were a few branch points further away. Similarly, A. sulcata was included in the Korean study, but shown to be more distantly related to B. trigonus.

Two possible phylogenetic trees for B. trigonus.
align=center|caption=After Bae et al, 2021 – Korean study	1=	1=Read more Source: Wikipedia, article Balanus trigonus. Content adapted from Wikipedia, available under the CC BY-SA 4.0 license. Accessed on 17/07/2026. Geographic distribution Native Exotic Loading map... ✖ • 1 record - • 2 or 3 records - • 4 to 10 records - • 11 to 50 records - • Over 51 records Species photographs Last published photographs  Add a photography of this species Species vocalizations Last vocalizations published  Add an audio of this species Species videos Last filmings published  Add a film of this species Species reports  Detail of places sorted by number of records Species records Count: 2 Page 1 of 1 Record ID Date Exact time Country Province / department Place Filmed Photographed Recorded vocal Observed Heard Wounded or dead Number of individuals User or Bibliography Detail 1410115 22/07/2018 Argentina Buenos Aires Mar del Plata Nicolas Olejnik 1458659 15/08/2015 Argentina Buenos Aires Mar del Plata Nicolas Olejnik Page 1 of 1  Add a record of this species 📖 Recommended citation Please use the following reference when citing this species account. EcoRegistros. 2026. Balanus trigonus – Species account. Accessed from www.ecoregistros.org on 14/09/2026.