Extremely well preserved earliest Cretaceous radiolarians were recovered from a tuffaceous claystone sample collected from a seamount flank of the Mariana Trench's ocean-ward slope by the Japanese submersible “Shinkai 6500”. Several species and genera belonging to Entactinaria have been described previously by the present authors. This study is an addition to the continuing investigation of this fauna, and will introduce one new family Paracuboctostylidae belonging to Entactinaria. Two new genera, Paracuboctostylus and Neoshinkaiera, and four new species, P. tetrayurta, N. simplex, Shinkaiera pacifica and S. robusta, are described.