ABSTRACT
Knowledge of major cirripede taxa, from Darwin to the present, is reviewed. The parasitic groups Ascothoracica and Rhizocephala are not Cirripedia in the strict sence. They are best regarded as sister groups of the cirripedes, within the Maxillopoda, where all three can be grouped into the taxon Thecostraca.
The evolution of the ordinary barnacles, the order Thoracica, is reviewed in some detail and relatively minor changes proposed at the superfamilial level. Difficulties arise over the affinities between the burrowing barnacles, the Acrothoracica with the Thoracica. Present evidence suggests that the acrothoracicans may have preceded the most primitive of the known thoracicans, the Lepadomorpha, rather than having stemmed from them.
The origin the principal sessile suborder of Thoracica, the Balanomorpha is inspected; ‘Darwinian’ and ‘Aurivillian’ hypotheses involving Pollicipes, Capitulum and Scillaelepas as models for the pedunculate ancestor prove unsatisfactory. New data on adult morphology and post-larval ontogeny of the primitive sessile barnacles Chionelasmus and Brachylepas necessitate reconsideration of the long-forgotten ‘Woodwardian’ hypothesis that places Brachylepas at the stem of the sessile barnacles. The Brachylepadomorpha, Verrucomorpha and Balanomorpha form a monophyletic taxon. It is proposed that they be reunited as suborders under the available taxon, the Sessilia; concomitantly the pedunculate superfamilies take on subordinal status within the Pedunculata. More complete knowledge of Brachylepas shows how the arrangement of wall plates in verrucomorphans and balanomorphans evolved from a sessile, brachylepadomorphan-like ancestor. It also indicates the probable organization of the extinct pedunculate ancestor of all sessile barnacles and allows a hypothetical reconstruction to be made.
