Cladistic analysis of the Cirripedia Thoracica

Abstract

We present a cladistic analysis of the Cirripedia Thoracica using morphological characters and the Acrothoracica and Ascothoracida as outgroups. The list of characters comprised 32 shell and soft body features. The operational taxonomic units (OTUs) comprised 26 well‐studied fossil and extant taxa, principally genera, since uncertainty about monophyly exists for most higher ranking taxonomic units. Parsimony analyses using PAUP 3.1.1 and Hennig86 produced 189 trees of assured minimal length. We also examined character evolution in the consensus trees using MacClade and Clados. The monophyly of the Balanomorpha and the Verrucomorpha sensu stricto is confirmed, and all trees featured a sister group relationship between the ‘living fossil Neoverruca and me Brachylepadomorpha. In the consensus trees the sequential progression of ‘pedunculate‘sister groups up to a node containing Neolepas also conforms to current views, but certain well‐established taxa based solely on plesiomorphies stand out as paraphyletic, such as Pedunculata (= Lepadomorpha); Eolepadinae, Scalpellomorpha and Chthamaloidea. The 189 trees differed principally in the position of shell‐less pedunculates, Neoverruca, the scalpelloid Capitulum, and the interrelationships within the Balanomorpha, although the 50% majority rule consensus tree almost fully resolved the latter. A monophyletic Sessilia comprising both Verrucomorpha and Balanomorpha appeared among the shortest trees, but not in the consensus. A tree with a monophyletic Verrucomorpha including Neoverruca had a tree length two steps longer than the consensus trees. Deletion of all extinct OTUs produced a radically different tree, which highlights the importance of fossils in estimating cirripede phylogeny. Mapping of our character set onto a manually constructed cladogram reflecting die most recent scenario of cirripede evolution resulted 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 transition from ‘pedunculate‘to ‘sessile‘barnacles. The inclusion of more fossil species at this point in our understanding of cirripede phylogeny will only result in even greater levels of uncertainty. When constructing the character list we also identified numerous uncertainties in the homology of traits commonly used in discussing cirripede evolution. Our study highlights larval ultrastructure, detailed studies of early ontogeny, and molecular data as the most promising areas for future research.

The Catophragmidae: members of the basal balanomorph radiation.

“…5 represents the first tree. The incremental acquisition in total number of major calcareous plates (character 2) supports the node leading to the chionelasmatids and beyond and is in fundamental agreement with the fossil record (Glenner et al, 1995). The general topology of our tree is in concordance with trees developed by Glenner et al (1995).…”

“…The incremental acquisition in total number of major calcareous plates (character 2) supports the node leading to the chionelasmatids and beyond and is in fundamental agreement with the fossil record (Glenner et al, 1995). The general topology of our tree is in concordance with trees developed by Glenner et al (1995). As anticipated on morphological and biogeographical grounds, Catolasmus is the sister group to Catophragmus and these two genera, with Catomerus, occur in the crown of the tree, or the derived members of the basal balanomorph radiation.…”

“…Although Wisely and Blick (1964) did not record the size of the individuals they examined, Egan and Anderson (1989) Darwin, 1852;Woodward, 1901;Withers, 1928;Newman et al, 1969;Newman, 1982;Anderson, 1994;Glenner et al, 1995). We do subscribe to a scalpellomorph ancestry for the brachylepadomorphs and hence to the balanomorphs (Newman, 1982(Newman, , 1987Buckeridge, 1996a: fig.…”

“…Cladistic analyses by Glenner et al (1995) and Buckeridge (1996a) were not designed specifically to resolve relationships among the genera we have selected for analysis, nor to resolve intrinsic relationships among the catophragmids and other basal balanomorphs.…”

Redescription of Scalpellopsis Striatociliata Broch, 1922, with a Discussion on Its Phylogenetic Position and the Peduncular Plate Pattern in Scalpellids

“…The Calanticidae are considered the sistergroup of the Scalpellidae (Glenner et al, 1995), the species of which have a well-developed rostrum, and most species of Euscalpellum have a plate in the rostro-lateral position. The rostrum in calanticids is well developed, whereas the presence or absence of the rostrum occurs in several genera of scalpellids (e.g., Arcoscalpellum).…”