title: Crawling through time: Transition of snails to slugs dating back to the Paleozoic, based on mitochondrial phylogenomics.
abstract: Sea slugs (Gastropoda: Opisthobranchia) are characterized by extensive morphological homoplasy. In particular, reduced or absent shells are predominant throughout the group. This trend towards shell loss has resulted in a poor fossil record. DNA-based phylogenies have been helpful in improving our understanding of the evolution of this group and major clades are emerging. We report 13 new complete opisthobranch mitochondrial genomes that provide robust support for some of these emerging nodes. We name three new clades within the Opisthobranchia, the Actopleura (Acteonoidea plus Nudipleura), Placoesophaga (Cephalaspidea plus Anaspidea), and Siphoglossa (Sacoglossa plus the Siphonaria). Finally we use molecular clock dating that suggests an earlier opisthobranch divergence than previously reported. The implications of this evolutionary scenario are discussed.
authors.affiliation: Evolutionary Genomics, DOE Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA 94598, USA. mmedina@ucmerced.edu
authors.forename: Mónica
authors.initials: M
authors.lastname: Medina
authors.forename: Shruti
authors.initials: S
authors.lastname: Lal
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Vallès
authors.forename: Tori L
authors.initials: TL
authors.lastname: Takaoka
authors.forename: Benoît A
authors.initials: BA
authors.lastname: Dayrat
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Boore
authors.forename: Terrence
authors.initials: T
authors.lastname: Gosliner
mesh_terms: D000818:Animals; D005075:Biological Evolution; D049851:Gastropoda / Q000033:anatomy & histology / Q000235:genetics*; D023061:Gene Order; D054629:Genome, Mitochondrial / Q000235:genetics*; D023281:Genomics / Q000379:methods*