Meeting Abstract

S10-2.1  Saturday, Jan. 7  Deep phylogeny and character evolution in the Thecostraca barnacles PEREZ-LOSADA, M*; HOEG, JT; ACHITUV, Y; CRANDALL, KA; CIBIO, University of Porto, Portugal; University of Copenhagen, Denmark; Bar Ilan University, Israel; Brigham Young University, USA

The Thecostraca is a highly advanced class of Crustacea. All have pelagic larvae and permanently sessile adults, but the individual taxa differ significantly in comprising both suspensions feeders and various types of parasites. A combined molecular analysis of major Thecostraca groups has allowed us for the first time to study the evolution of morphological structures and life styles in the group as a whole and in the Cirripedia Thoracica in particular. Our analyses focus on key features such as the cypris larva, suspension feeding, parasitism, shell plate armament, body shape and sexual systems. Our phylogenies indicate that the Cirripedia are monophyletic with the Ascothoracida and Facetotecta clades as successive outgroups. Using this phylogenetic framework and Bayesian methods of character reconstruction we observed that: 1) amoeboid metamorphic stages found both in the endoparasitic Rhizocephala and the presumed endoparasitic Facetotecta are convergent; 2) suspension feeding is probably plesiomorphic for all cirripeds; 3) within the Thoracica, 5-plated and naked forms evolved from multiplated ancestors, thus contradicting traditional interpretations based on fossil and ontogeny evidence; 4) asymmetric barnacles are not monophyletic since the deep sea neoverrucids do not cluster with the verrucids, which are part of the Sessilia clade together with the Balanomorpha; 5) dioecy (separate sexes) is ancestral in the Cirripedia and hermaphroditism evolved in the stem line leading to the Thoracica, although subsequent evolution of reproductive systems within the latter is complex and will require further study.