CLADISTIC-ANALYSIS OF THE CIRRIPEDIA-THORACICA

We present a cladistic analysis of the Cirripedia Thoracica using morp hological characters and the Acrothoracica and Ascothoracida as outgro ups. The list of characters comprised 32 shell and soft body features. The operational taxonomic units (OTUs) comprised 26 well-studied foss il and extant taxa, principally genera, since uncertainty about monoph yly exists for most higher ranking taxonomic units. Parsimony analyses using PAUP 3.1.1 and Hennig86 produced 189 trees of assured minimal l ength. We also examined character evolution in the consensus trees usi ng MacClade and Clados. The monophyly of the Balanomorpha and the Verr ucomorpha sensu stricto is confirmed, and all trees featured a sister group relationship between the 'living fossil' Neoverruca and the Brac hylepadomorpha. In the consensus trees the sequential progression of ' pedunculate' sister groups up to a node containing Neolepas also confo rms to current views, but certain well-established taxa based solely o n plesiomorphies stand out as paraphyletic, such as Pedunculata (=Lepa domorpha); Eolepadinae, Scalpellomorpha and Chthamaloidea. The 189 tre es differed principally in the position of shell-less pedunculates, Ne overruca, the scalpelloid Capitulum, and the interrelationships within the Balanomorpha, although the 50% majority rule consensus tree almos t fully resolved the latter. A monophyletic Sessilia comprising both V errucomorpha and Balanomorpha appeared among the shortest trees, but n ot in the consensus. A tree with a monophyletic Verrucomorpha includin g Neoverruca had a tree length two steps longer than the consensus tre es. Deletion of all extinct OTUs produced a radically different tree, which highlights the importance of fossils in estimating cirripede phy logeny. Mapping of our character set onto a manually constructed clado gram reflecting the most recent scenario of cirripede evolution result ed in a tree length five steps longer than any of our shortest trees. Our analysis reveals that several key questions in cirripede phylogeny remain unsolved, notably the position of shell-less forms and the tra nsition from 'pedunculate' to 'sessile' barnacles. The inclusion of mo re fossil species at this point in our understanding of cirripede phyl ogeny will only result in even greater levels of uncertainty. When con structing the character list we also identified numerous uncertainties in the homology of traits commonly used in discussing cirripede evolu tion. Our study highlights larval ultrastructure, detailed studies of early ontogeny, and molecular data as the most promising areas for fut ure research. (C) 1995 The Linnean Society of London