TAXONOMY AND EVOLUTION OF PALEOGENE ANTARCTIC AND TROPICAL LOPHOCYRTID RADIOLARIANS

Investigation of three-segmented theoperids through successive stratig raphic levels in Antarctic Paleogene sediment sequences, and a tropica l reference section, resulted in recognition of four groups characteri zed by different cephalic structures taxonomically treated as the new genera, Aphetocyrtis and Clinorhabdus, the new subgenus Lophocyrtis (A poplanius), and the previously described subgenus Lophocyrtis (Lophocy rtis). All four lineages are represented in Middle Eocene sediments fr om the Antarctic. The Antarctic representatives of the tropical Lophoc yrtis (Lophocyrtis) lineage become extinct at the end of the Middle Eo cene. The diversity of the two new genera, restricted to the Antarctic , is at a peak in the Oligocene interval, coincident with the major co oling event reported during this interval. Most of the new species are endemic to the Antarctic, and only three have been sporadically found in rare abundance in tropical areas. One geographic invasion from the tropics to the Antarctic is documented. The following ten new taxa ar e described: Aphetocyrtis gnomabax, A., catalexis, A. rossi, Lophocyrt is (Apoplanius) nomas, L. (A.) keraspera, L. (A.) klydus, Lophocyrtis (Lophocyrtis) jacchia; hapsis, Lophocyrtis (Lophocyrtis ?) zeira, Clin orhabdus anantomus and C. ocymora. Species whose definitions have been emended herein are: Lophocyrtis (Apoplanius) aspera, Lophocyrtis (Lop hocyrtis) jacchia jacchia, L. (L. ?) barbadense, L. (L. ?) semipolita, Clinorhabdus longithorax and C. robusta.