Asymmetrical thoracican cirripedes of superfically similar ‘verrucomorph’ morphology are shown to have evolved independently three times from pedunculate ancestors. In each case, the loss of a peduncle was accompanied by preferential attachment on one side or the other, such that the rostrum, carina and one of each paired scuta and terga (fixed) formed a wall-like structure; the opposite scutum and tergum (free or moveable) transforming into an opercular lid closed by the scutal adductor muscle. True verrucomorphs (Eoverruca + Verrucidae) have their origin in the mid-Cretaceous sessile genera Pycnolepas and Faxelepas gen. nov., which demonstrate a marked, but facultative, tendency towards capitular asymmetry, confirmed by strong morphological similarities in plate morphology to the basal verrucomorph genus Eoverruca of Late Cretaceous age. Proverruca, another Late Cretaceous asymmetrical form, is not closely related; it evolved independently from a scalpelliform ancestor. The extant hydrothermal vent genera Neoverruca and Imbricaverruca evolved from symmetrical scalpelliforms of the family Neolepadidae, as demonstrated by both molecular and morphological evidence. Cladistic analysis of 38 characters in 14 living and fossil taxa has yielded a consensus tree showing a monophyletic Verrucomorpha, made up of a stem group (Eoverruca) and crown group (Verrucidae). Faxelepas bruennichi comb. nov. and Pycnolepas rigida are sister taxa to the Verrucomorpha, and evolved from a pedunculate ancestor. The Verrucidae are divided into a basal stem group (Altiverruca, Globosoverruca) and a derived crown group (all other genera). Within the crown group, the monophyletic Priscoverrucinae subfam. nov. is identified. Systematic revision of Cretaceous verrucomorphs and basal sessilians includes description of Pedupycnolepas gen. nov., Faxelepas gen. nov., Youngiverruca gen. nov. and Priscoverruca gen. nov. and two new species, Youngiverruca ruegenensis sp. nov. and Verruca jagti sp. nov. The development of asymmetry was perhaps a feeding adaptation, enabling barnacles to catch crawling benthic prey in deep ocean environments where food is scarce.
- fossil taxonomy