Axonemal microtubule pattern of Cienkowskya mereschkovskyi and a revision of heliozoan taxonomy

Abstract

Cienkowskya mereschkovskyi is a spherical heliozoan with a mucous stalk and a cell coat with spicules randomly distributed. The axonemal microtubules arise from a central MTOC with a centroplast. The microtubular pattern displays a triradial symmetry and is characterized in cross-section by one central hexagon with alternate angles of 106° and 134°. From this slightly irregular central pattern, convex branches made of a series of microtubules and linkers diverge. Any three microtubules (Mt's) along the branch form 166° angles. Around the central hexagon links between successive branches always delineate 3 pairs of enneagons and 3 heptagons, while the peripheral polygons are less strictly defined. None of the previously published theories on Mt-pattern formation are sufficient to totally explain such a complex pattern. A comparison between the fine structure of Cienkowskya and other Heliozoa with reference to very recent data leads us to try to amend the existing terminology for the substructure of the MTOC. An attempt at a more coherent classification is also made using electron microscopy criteria with new arguments compared to existing ones (Febvre-Chevalier, 1982, 1983). A taxonomical key comprising several new names is proposed. © 1984 D. Reidel Publishing Company.