title: Fine Structure and Molecular Phylogeny of Parametopidium circumlabens (Ciliophora: Armophorea), Endocommensal of Sea Urchins.
abstract: Metopid armophoreans are ciliates commonly found in anaerobic environments worldwide; however, very little is known of their fine structure. In this study, the metopid Parametopidium circumlabens (Biggar and Wenrich 1932) Aescht, 1980, a common endocommensal of sea urchins, is investigated for the first time with emphasis on transmission electron microscopy, revealing several previously unknown elements of its morphology. Somatic dikinetids of P. circumlabens have a typical ribbon of transverse microtubules, an isolated microtubule near triplets 4 and 5 of the anterior kinetosome, plus two other microtubules between anterior and posterior kinetosomes, a short kinetodesmal striated fiber and long postciliary microtubules. In the dikinetids of the perizonal stripe, the kinetodesmal fiber is very pronounced, and there is a conspicuous microfibrillar network system associated with the kinetosomes. A new structure, shaped as a dense, roughly cylindrical mass surrounded by microtubules, is found associated with the posterior kinetosome of perizonal dikinetids. The paroral membrane is diplostichomonad and the adoral membranelles are of the "paramembranelle" type. Bayesian inference and maximum-likelihood analysis of the 18S-rDNA gene unambiguously placed P. circumlabens as sister group of the cluster formed by ((Atopospira galeata, Atopospira violacea) Metopus laminarius) + Clevelandellida, corroborating its classification within the Metopida.
authors.affiliation: Laboratório de Protistologia, Dept. de Zoologia, Inst. de Biologia, CCS A:074, Universidade Federal do Rio de Janeiro - UFRJ, CEP: 21941-590, Ilha do Fundão, Rio de Janeiro, Brazil.
authors.forename: Inácio Domingos
authors.initials: ID
authors.lastname: da Silva-Neto
authors.affiliation: Laboratório de Protistologia, Dept. de Zoologia, Inst. de Biologia, CCS A:074, Universidade Federal do Rio de Janeiro - UFRJ, CEP: 21941-590, Ilha do Fundão, Rio de Janeiro, Brazil.|Laboratório de Biologia Molecular "Francisco Mauro Salzano", Inst. de Ciências Biológicas, Universidade Federal do Pará - UFPA, CEP: 66075-110, Belém, Pará, Brazil.
authors.forename: Thiago
authors.initials: T
authors.lastname: da Silva Paiva
authors.affiliation: Centro de Tecnologia Agropecuária, Ins. Socioambiental e dos Recursos Hídricos, Universidade Federal Rural da Amazônia - UFRA, CEP: 66077-901, Belém, Pará, Brazil.
authors.forename: Bárbara
authors.initials: B
authors.lastname: do Nascimento Borges
authors.affiliation: Laboratório de Biologia Molecular "Francisco Mauro Salzano", Inst. de Ciências Biológicas, Universidade Federal do Pará - UFPA, CEP: 66075-110, Belém, Pará, Brazil.
authors.forename: Maria Lúcia
authors.initials: ML
authors.lastname: Harada
mesh_terms: D000818:Animals; D064652:Basal Bodies / Q000648:ultrastructure; D001499:Bayes Theorem; D016798:Ciliophora / Q000145:classification / Q000235:genetics* / Q000502:physiology / Q000648:ultrastructure*; D008854:Microscopy, Electron; D008870:Microtubules / Q000648:ultrastructure; D010802:Phylogeny; D012617:Sea Urchins; D017422:Sequence Analysis, DNA; D013559:Symbiosis
keywords: Benthos; Lytechinus; Metopida; Parametopus; Tripneustes