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eage was fully aerobic (Hall and Luck, 1995). In trophic forms of protists that lack mastigote stages, the karyomastigont is generally absent. An exception is Histomonas, an amoeboid trichomonad cell that lacks an axoneme but bears enough of the remnant karyomastigont structure to permit its classification with parabasalids rather than with rhizopod amoebae (Dyer, 1990). This organellar system appears in the zoospores, motile trophic forms, or sperm of many organisms, suggesting the relative ease of karyomastigont development. The karyomastigont, apparently in some cells, is easily lost, suppressed, and regained. In many taxa of multinucleate or multicellular protists (foraminifera, green algae) and even in plants, the karyomastigont persists only in the zoospores or gametes.

In yeast, nematode, insect, and mammalian cells, nonkaryomastigont microtubule-organizing centers are “required to position nuclei at specific locations in the cytoplasm” (Raff, 1999). The link between the microtubule organizing center and the nuclei “is mysterious” (Raff, 1999). To



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