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Abstract

The long-ranging Early to Middle Triassic coniform conodont form-genus Cornudina Hirschmann occurs abundantly in the Anisian of NW Turkey, Northern Tethys. Although suggested to represent the P1 element of an apparatus of the Order Ozarkodinida Dzik, questions concerning the apparatus of Cornudina remain. A description of the probable phylogenetic trends in the P1 elements of Cornudina is attempted and the role of the form-genera Ketinella Gedik and Kamuellerella Gedik, as the alternative ramiform skeletal elements in the Cornudina multi-element apparatus, is investigated. The newly described, Gedikella quadrata gen. nov., sp. nov., is an S element, Kamuellerella rectangularis sp. nov., is either an S3 or an S4 element, and Ketinella goermueshi sp. nov., is an M element.
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Abstract

The paper reports a comparative study of the female gametophyte and especially synergid structure in sexual and apomictic dandelions. We analyzed diploid sexually reproducing Taraxacum linearisquameum (2n = 2x = 16) and two triploids, T. alatum and T. udum (2n = 3x =24), with autonomous embryo and endosperm development. There were no observed differences in the organization of the mature megagametophyte between the examined species. Both meiotically reduced and diplosporous embryo sacs showed typical polarity of the egg apparatus cells, together with development of a filiform apparatus in the synergids, but immunocytochemical analyses indicated that microtubules form longitudinal brush-like bundles adjacent to the filiform apparatus in the synergids of the sexual T. linearisquameum. This arrangement of cytoskeletal elements is similar to the configuration described in other amphimictic plants. The synergids of the apomictic T. alatum and T. udum show a uncharacteristic and relatively weak cytoskeleton with no brush-like bundles. We discuss the role of synergids in autonomous apomicts.
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