Phylogenetics and morphological evolution of coral‐dwelling barnacles (Balanomorpha: Pyrgomatidae)

Pyrgomatid barnacles are a family of balanomorphs uniquely adapted to symbiosis on corals. The evolution of the coral‐dwelling barnacles is explored using a multi‐gene phylogeny (COI, 16S, 12S, 18S, and H3) and phenotypic trait‐mapping. We found that the hydrocoral associate Wanella should be excluded, while some archaeobalanids in the genus Armatobalanus should be included in the Pyrgomatidae. Three well supported clades were recovered: clade I is the largest group and is exclusively Indo‐West Pacific, clade II contains two plesiomorphic Indo‐West Pacific genera, while clade III is comprised of East and West Atlantic taxa. Some genera did not form reciprocally monophyletic groups, while the genus Trevathana was found to be paraphyletic and to include members of three other apomorphic genera/tribes. The highly unusual coral‐parasitic hoekiines appear to be of recent origin and rapidly evolving from Trevathana sensu lato. Pyrgomatids include six‐, four‐, and one‐plated forms, and exhibit convergent evolutionary tendencies towards skeletal reduction and fusion, loss of cirral armature, and increased host specificity. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113, 162–179.