Kojiro Nakaseko

The cephalic skeletal structure of Jurassic “Eucyrtidium” (Radiolaria)

Almost all nassellarians possess some skeletons, comprised of cephalic skeletal elements, at the base of their cephalis. Observations using the scanning electron microscope (SEM) have been made on the internal structures of Jurassic “Eucyrtidium” from manganese carbonate ore deposits in the Mino Terrane, central Japan. Jurassic “Eucyrtidium” possesses only a median bar and apical spine as cephalic skeletal elements. Because this structure is quite different from that of Cenozoic Eucyrtidium , which possess MB, A, V, L, l, and D, a new genus, Monosera , is proposed for the Jurassic forms. One new species, Monosera gujoensis , is described.