755. TWO NEW JURASSIC GENERA OF FAMILY PALAEOSCENIDIIDAE (RADIOLARIA)

Abstract

Exceedingly well-preserved Jurassic radiolarians have been obtained from manganese ore deposits in the Mino Belt, central Japan. Among them, two species of family Palaeoscenidiidae, Hilarisirex quadrangularis n. gen., n. sp. and Diceratigalea hemisphaera n. gen., n. sp., which have a median bar, two apical spines and four basal spines, are described. They also belong to Nassellaria, because their tests are composed of cephalis and thorax, and possess cephalic skeletal elements. The new subfamily Hilarisisirecinae has been created for these two new genera. Consequently, taxonomic position of family Palaeoscenidiidae must be re-examinned. This family may be regarded as an ancestor of Nassellaria. Also, it is possible that Nassellaria in the current classification is a polyphyletic taxon. The definition of Nassellaria must be re-examined. A lineage of "Paleozoic Palaeoscenidiids→Hilarisirex quadrangularis→Diceratigalea hemisphaera" is proposed. If this process of evolution is correct, the most important taxonomic criterion of Nassellaria is the pattern of cephalic skeletal structure.