Get this from a library! Cours de zoologie. Fascicule I, Protozoaires, spongiaires, cnidaires, plathelminthes, némathelminthes. [Pierre Binet]. Le cours consiste en une mise au point synthétique sur les cnidaires récifaux ( morphologie, biologie, systématique, fonctionnement des symbioses. thématique du colmatage des cours d’eau par les sédiments fins ainsi que sur sa Les pourcentages des groupes d’invertébrés, Cnidaires, Triclades.
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The early diverging metazoan lineages have highly disparate adult body plan geometries, which can be characterised in terms of five major types of symmetry asymmetrical, spherical, cylindrical, n -radial, bilateral.
Patterns of evolutionary changes in symmetry types and the homology of body axes across lineages are discussed here by confronting evidence from comparative anatomy, phylogeny, genomics and evo-devo. The conventional scenario, postulating a graded complexification from asymmetry to radial and finally bilateral symmetry, is considered untenable.
Cylindrical symmetry is likely cojrs be the ancestral type from which derived all remaining types through multiple convergences.
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Recent proposals prompted by molecular data that the bilateral anatomies of many cnidarians and of the Bilateria are homologous are clearly not supported.
The Hox-based patterning system operating along the antero-posterior axis of the Bilateria does not seem to predate their divergence with the Cnidaria, but intercellular signalling systems, notably the Wnt pathway, could have been involved in generating the main body axis in the last common ancestor of fnidaires Metazoa.
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If you are a subscriber, please sign in ‘My Account’ at the top right of the screen. If you want to subscribe to this journal, cniidaires our rates You can purchase this item in Pay Per View: Early evolution of symmetry and polarity in metazoan body plans.
Outline Masquer le plan. Definition of symmetry and polarity.
Types of symmetry and body polarity axes: On the biological significance of the various types of symmetry. Did evolutionary transitions between symmetry types reflect shifts in organism coues Reconstructing the early evolution of symmetry types: The metazoan ancestor was probably cylindrically symmetrical.
Anatomical comparison of the bilateral symmetry in anthozoans and bilaterians. Developmental genes and the homology of polarity axes: Hox genes and the correspondence between the cnidarian oral—aboral axis and the bilaterian AP axis.
Wnt signalling molecules and the ancestral polarity axis. Top of the page – Article Outline.