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Diapositiva 1 Rhopalura Orthonectido Lección 21.- Los Diciémidos y Ortonéctidos. Descripción anatómica y de su ciclo biológico. Posición filogenética. Evolución histórica del concepto de Mesozoos. Mesozoos: ortonéctidos y rombozoos 1. Originalmente el filo Mesozoa fue creado para los Dicyemidos (Rombozoos), a los cuales se otorgó una posición intermedia entre protozoos y metazoos. 2. Posteriormente se incluyeron los Ortonéctidos y otros animales de difícil ubicación sistemática, generalmente organismos paucicelulares de estructura muy sencilla. 3. DELAGE los dividió en 4 grupos: mesogonia (dicyemidos y ortonéctidos), mesogastria (Salinella), mesocelia (Penmatodiscus) y mesenquimia (Trichoplax). 4. En la actualidad solamente los Dicyemidos y Ortonéctidos se consideran bajo el término mesozoos. Saliniella salve LOS MESOZOOS Phylum Mesozoa (van Beneden, 1876) Cl. Mesogonia o Moruloidea Or. Rombozoos (diciémidos) Or. Ortonéctidos Phylum Mesozoa Cl. Rombozoos Cl. Ortonéctidos Phylum Rhombozoa “mesozoos” Phylum Orthonectida Biología de Mesozoos: http://www.cephbase.utmb.edu/refdb/pdf/7851.pdf ORTONECTIDOS • Son parásitos de invertebrados (equinodermos, anélidos, …) • Los adultos llevan vida libre, nadan en línea recta por el batido de los cilios • Son de sexos separados, excepcionalmente los hay hermafroditas • Las ♀ son aplanadas, cuerpo cubierto por cilios • Los ♂ y ♀ cuando están maduros salen del hospedador y se juntan • Los espermatozoides pasan dentro del cuerpo de la ♀ para fecundarla • La segmentación lleva a una pequeña larva llamada a veces MORULOIDE cubierta de cilios Plasmodio Morula • Cuando la larva Moruloide está bien formada sale del cuerpo de la ♀ y penetra en el hospedador (bursas de ofiuras, planarias, nemertinos) • La mórula se transforma en una serie de plasmodios que invaden el tejido genital de la ofiura • En un momento dado, a partir de algunos núcleos del plasmodio se van a formar nuevos individuos • Cada plasmodio es UNIXESUAL y los nuevos individuos que lleva dentro todos son del mismo sexo • Los individuos salen por ruptura del plasmodio y comienza en ciclo Ph. Mesozoa: Cl. Ortonéctidos Rhopalura ophiocomae Ciliocincta sabellariae Ph. Mesozoa: Cl. Rombozoos Cl. Rombozoos Or. Dicyemida (Dicyema, Pseudicyema, Dicyemennea) Or. Heterocyemida (Microcyema, Conocyema) Microcyema Conocyema ROMBOZOOS Dicyema Pseudodicyema Dicyemenna Diapolares Células Axial Axoblastos • Son parásitos de Sifonóforos, raramente en el calamar • Viven en la orina, alimentándose por endocitosis por fusión de microvellosidades • Las fases parásitas son anaeróbicas y las fases libres aeróbicas Dicyema • El individuos típico de un Dicyemido se llama NEMATÓGENO Primario • El número de células del somatodermo y su disposición es constante • El ápice suele tener 10 células: 2 parapolares, 4 metapolares y 4 propolares • Las células del tronco se llaman todas “diapolares”, excepto las dos últimas que se llaman “uropolares” • En el interior del cuerpo de un Dicyemido aparece una gran célula: “Células Axial” • Centro de la Célula Axial se localizan células más pequeñas, los “axoblastos” que están reproduciéndose para formar: nuevos axoblastos y larvas que saldrán del nematógeno y formarán un nuevo individuo, que cuando esté bien formado sale de la célula axial y del nematógeno Ciclo Biológico de Diciémidos Célula Axial Axoblasto Célula Axial Axoblasto 1. La entrada del Rombozoos tiene lugar en los pulpos jóvenes. Esta infección la realiza un individuo muy sencillo llamado larva fundadora de procedencia desconocida 2. La Larva Fundadora se caracteriza por tener el cuerpo pequeño, en el interior tiene 3 cél. Axiales y 1 axoblasto en cada una 3. Esta larva fundadora crece y origina el Nematógeno Fundador que tiene 3 cél. Axiales y numerosos axoblastos en su interior. 4. Cada uno de los Axoblastos se divide en células pequeñas, medianas y grandes y dan la Larva Vermiforme con una célula Axial y un Axoblasto en su interior Ciclo Biológico de Diciemidos (continuación-II) Larva Vermiforme Células Axial Axoblastos Células Axial Axoblastos 1. El Axoblasto de la Célula Axial de la Larva Vermiforme se multiplica muchas veces y como consecuencia la Larva Vermiforme se transforma en Nematógeno Primario 2. Estos Nematógenos Primarios son los que propagan la infección a través de la orina. 3. La única célula axial del Nematógeno Primario lleva axoblastos que producirán nuevas Larvas Vermiformes y estas nuevos Nematógenos Primarios en Generaciones Sucesivas 4. Estas Generaciones Sucesivas de Nematógenos Primarios suceden hasta que el pulpo alcanza la madurez sexual. En este momento los Axoblastos de la célula Axial produce otro individuos llamado ROMBÓGENO 5. Los Rombógenos son los encargados de realizar la Fase Sexual del ciclo Ciclo Biológico de Diciemidos (continuación-III) Axoblastos Rombógeno 1. Cada Axoblasto del Rombógeno se divide en 2 células, una Grande (G) y otra Pequeña (P) 2. La célula Pequeña desaparece, y la que queda, la G, se vuelve a dividir, dando otra Grande (G) y otra Mediana (M) que no se divide 3. La célula G se vuelve a dividir, y da una Grande y otra Pequeña (P) 4. Las células Pequeñas se meten dentro de la Grande, mientras que la Mediana se divide con mucha rapidez y forma un anillo que rodea a la célula Grande 5. La célula Pequeña que estaba dentro de la Grande se divide muy rápidamente originando numerosos espermatozoides 6. A la vez que ocurre esto, las células de la cubierta (Medianas) se transforman en ÓVULOS 7. A este nuevo individuo se llama INFUSIRÓGENO, que es hermafrodita 8. Cada espermatozoide fecunda a un óvulo, y una vez fecundados quedan libres en el interior de la célula Axial 9. Por crecimiento de estos ÓVULOS fecundados se llega a un estado llamado LARVA INFUSORIFORME que aún está dentro de la célula Axial de los Rombógenos Ciclo Biológico de Diciemidos (continuación-IV) 1. La Larva Infusoriforme tienen un par de células grandes sin cilios anteriores y en su interior tienen un hueco 2. Las células grandes del interior de la Larva Infusoriforme producen enzimas que van digiriendo la célula Axial y la larva sale del Rombógeno 3. El Rombógeno tiene capacidad para cicatrizar esta ruptura producida por la salida de la larva y formar nuevas larvas 4. Las larvas una vez fuera del Rombógeno salen al exterior por la orina del pulpo y no se sabe lo que pasa después The phylogenetic position of Rhopalura ophiocomae (Orthonectida) based on 18S ribosomal DNA sequence analysis. Hanelt B, Van Schyndel D, Adema CM, Lewis LA, Loker ES. Department of Biology, University of New Mexico, Albuquerque 87131, USA. The Orthonectida is a small, poorly known phylum of parasites of marine invertebrates. Their phylogenetic placement is obscure; they have been considered to be multicellular protozoans, primitive animals at a "mesozoan" grade of organization, or secondarily simplified flatworm-like organisms. The best known species in the phylum, Rhopalura ophiocomae, was collected on San Juan Island, Wash. and a complete 18S rDNA sequence was obtained. Using the models of minimum evolution and parsimony, phylogenetic analyses were undertaken and the results lend support to the following hypotheses about orthonectids: (1) Orthonectids are more closely aligned with triploblastic metazoan taxa than with the protist or diploblastic metazoan taxa considered in this analysis (2) Orthonectids are not derived members of the phylum Platyhelminthes (3) Orthonectids and Rhombozoans are not each other's closest relatives, thus casting further doubt on the validity of the phylum Mesozoa previously used to encompass both groups. PMID: 8896370 [PubMed - indexed for MEDLINE] Mol Biol Evol. 1996 Nov;13(9):1187-91 Phylogenetic position of the dicyemid mesozoa inferred from 18S rDNA sequences. Katayama T, Wada H, Furuya H, Satoh N, Yamamoto M. Ushimado Marine Laboratory, Okayama University, Japan. The dicyemid mesozoa, obligate symbionts in the cephalopod kidney, are simply organized multicellular animals. They have long been the subject of phylogenetic debates. Some authors have suggested that dicyemids represent an offshoot from an early metazoan ancestor. Other workers considered them to be degenerated progeny of higher metazoa, possibly parasitic trematodes. We determined the almost complete nucleotide sequences of 18S rDNA in two species of dicyemid, Dicyema orientale and Dicyema acuticephalum, isolated purely from cephalopod urine. We compared these sequences with sequences determined in the present study from three flatworm species, as well as with a variety of eukaryote sequences obtained from databases. The phylogenetic trees reconstructed with the use of the neighbor-joining, maximum-parsimony, and maximum-likelihood methods indicated that the dicyemids belong among the triploblastic animals (Bilateria). However, we cannot firmly establish the position of the dicyemids within the Bilateria because we cannot ignore the problem of long branch attraction between the myxozoans, dicyemids, nematodes, and acoel flatworms. The present results favor the hypothesis that the Dicyemids do not represent an early divergent metazoan group, but rather a group degenerated from a triploblastic ancestor. Biol Bull. 1995 Oct-Nov;189(2):81-90. Su relación con platelmintos, al menos en el caso de los dicyemidos, se ve apoyada por numerosos análisis basados en datos moleculares (KATAYAMA et al. 1995; VAN DE PEER y DE WACHTER, 1997; KOBAYASHI, FURUYA y HOLLAND, 1999) Salinella salve MESOZOOS. Desde el punto de vista de sus relaciones de parentesco, diferentes autores los han
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