title: A molecular and karyological approach to the taxonomy of Nautilus.
abstract: Nautiloids, the externally shelled cephalopods of Cambrian origin, are the most ancient lineage among extant cephalopods. Their ancestral characters are explored based on morphological and molecular data (18S rDNA sequence) to investigate the evolution of present cephalopod lineages. Among molluscs, nautilus 18S rDNA gene is the longest reported so far, due to large nucleotidic insertions. By comparison with other 18S sequences, the complete gene of N. macromphalus helps to clarify the taxonomic status of the three universally recognised Nautilus species. The range of interspecific molecular differences supports separation of the present species into two surviving ectocochleate genera, Nautilus and Allonautilus. Nautiloid 18S is considered as corresponding to the ancestral form of 18S as is the number of chromosomes in Nautilus (52), the lowest among cephalopods. Comparison of karyological characteristics amongst cephalopods in a phylogenetic context suggests a possible correlation between duplication events and lineage divergence.
authors.affiliation: Département Milieux et Peuplements aquatiques, UMR 5178 (BOME), Muséum national d'histoire naturelle, Institut Jacques-Monod-CNRS, universités Paris-6 & -7, 2, Paris, France. bonnaud@ccr.jussieu.fr
authors.forename: Laure
authors.initials: L
authors.lastname: Bonnaud
authors.forename: Catherine
authors.initials: C
authors.lastname: Ozouf-Costaz
authors.forename: Renata
authors.initials: R
authors.lastname: Boucher-Rodoni
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002875:Chromosomes / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D005796:Genes; D007621:Karyotyping; D008969:Molecular Sequence Data; D008974:Mollusca / Q000145:classification* / Q000235:genetics; D009690:Nucleic Acid Conformation; D010802:Phylogeny; D012337:RNA, Ribosomal, 18S / Q000737:chemistry / Q000235:genetics; D016415:Sequence Alignment; D017385:Sequence Homology; D013045:Species Specificity
chemical_list: D004275:DNA, Ribosomal; D012337:RNA, Ribosomal, 18S