title: Origin of the Mesozoa inferred from 18S rRNA gene sequences.
abstract: The phylum Mesozoa comprises small, simply organized wormlike parasites of marine invertebrates and is composed of two classes, the Rhombozoa and the Orthonectida. The origin of Mesozoa is uncertain; they are classically considered either as degenerate turbellarians or as primitive multicellular animals related to ciliated protists. In order to precisely determine the phylogenetic position of this group we sequenced the complete 18S rRNA gene of one rhombozoid, Dicyema sp., and one orthonectid, Rhopalura ophiocomae. The sequence analysis shows that the Mesozoa branch early in the animal evolution, closely to nematodes and myxozoans. Our data indicate probably separate origins of rhombozoids and orthonectids, suggesting that their placement in the same phylum needs to be revised.
authors.affiliation: Département de Zoologie et Biologie animale, Université de Genève, Switzerland. pawlow@sc2a.unige.ch
authors.forename: J
authors.initials: J
authors.lastname: Pawlowski
authors.forename: J I
authors.initials: JI
authors.lastname: Montoya-Burgos
authors.forename: J F
authors.initials: JF
authors.lastname: Fahrni
authors.forename: J
authors.initials: J
authors.lastname: Wüest
authors.forename: L
authors.initials: L
authors.lastname: Zaninetti
mesh_terms: D000818:Animals; D005075:Biological Evolution; D016798:Ciliophora / Q000235:genetics; D007448:Invertebrates / Q000145:classification / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009348:Nematoda; D010271:Parasites / Q000145:classification / Q000235:genetics / Q000502:physiology; D010802:Phylogeny; D012337:RNA, Ribosomal, 18S; D012441:Saccharomyces cerevisiae / Q000235:genetics; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid
chemical_list: D012337:RNA, Ribosomal, 18S