title: On the origin of a novel parasitic-feeding mode within suspension-feeding barnacles.
abstract: In his monograph on Cirripedia from 1851, Darwin pointed to a highly unusual, plateless, and most likely parasitic barnacle of uncertain phylogenetic affinity. Darwin's barnacle was Anelasma squalicola, found on deep-water sharks of the family Etmopteridae, or lantern sharks. The barnacle is uncommon and is therefore rarely studied. Recent observations by us have shown that they occur at an unusually high prevalence on the velvet belly lantern shark, Etmopterus spinax, in restricted fjord areas of western Norway. A phylogenetic analysis based on ribosomal DNA data (16S, 18S, and 28S) from 99 selected barnacle species, including all available pedunculate barnacle sequences from GenBank, shows that A. squalicola is most closely related (sister taxon) to the pedunculate barnacle Capitulum mitella. Both C. mitella and species of Pollicipes, situated one node higher in the tree, are conventional suspension feeders from the rocky intertidal. Our phylogenetic analysis now makes it possible to establish morphological homologies between A. squalicola and its sister taxon and provides the evolutionary framework to explain the unprecedented transition from a filter-feeding barnacle to a parasitic mode of life.
authors.affiliation: Marine Biodiversity Group, Department of Biology, University of Bergen, Thormøhlensgate 53A, 5006 Bergen, Norway.
authors.forename: David John
authors.initials: DJ
authors.lastname: Rees
authors.affiliation: Marine Biodiversity Group, Department of Biology, University of Bergen, Thormøhlensgate 53A, 5006 Bergen, Norway.
authors.forename: Christoph
authors.initials: C
authors.lastname: Noever
authors.affiliation: Department of Biology, Marine Biological Section, University of Copenhagen, 2100 Copenhagen, Denmark.
authors.forename: Jens Thorvald
authors.initials: JT
authors.lastname: Høeg
authors.affiliation: Marine Biodiversity Group, Department of Biology, University of Bergen, Thormøhlensgate 53A, 5006 Bergen, Norway.
authors.forename: Anders
authors.initials: A
authors.lastname: Ommundsen
authors.affiliation: Marine Biodiversity Group, Department of Biology, University of Bergen, Thormøhlensgate 53A, 5006 Bergen, Norway; Center for Macroecology and Evolution, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark. Electronic address: henrik.glenner@bio.uib.no.
authors.forename: Henrik
authors.initials: H
authors.lastname: Glenner
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005247:Feeding Behavior; D006790:Host-Parasite Interactions; D008969:Molecular Sequence Data; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics / Q000378:metabolism; D012337:RNA, Ribosomal, 18S / Q000235:genetics / Q000378:metabolism; D012339:RNA, Ribosomal, 28S / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D012754:Sharks / Q000469:parasitology*; D001468:Thoracica / Q000235:genetics / Q000502:physiology*
chemical_list: D012336:RNA, Ribosomal, 16S; D012337:RNA, Ribosomal, 18S; D012339:RNA, Ribosomal, 28S