Latentifistularia and other radiolarian species from the lower Smithian (Lower Triassic) Lang Son Formation, NE Vietnam

Well-preserved Early Triassic radiolarians were recovered from lower Smithian (lower Olenekian) beds in NE Vietnam. The radiolarian assemblage consists only of Paleozoic relict species of Latentifistularia and some entactinarians. Three latentifistularian species, Ruzhencevispongus vietnamensis nov. sp., Tetragregnon chilangensis nov. sp., and Tetragregnon langsonensis nov. sp., belonging to the families Ruzhencevispongidae Kozur and Tetratormentidae Nestell and Nestell are erected herein. The entactinarian family Triassothamnidae nov. fam. and one new genus and two new species of Langsonsphaera pseudocubica nov. gen. nov. sp. and Stigmosphaerostylus amabilis nov. sp. are also described. In this region, the Paleozoic-type radiolarian groups Latentifistularia and Entactinaria survived across the Permian–Triassic boundary and were present during the Induan–early Olenekian interval. Thus, in the eastern Tethyan seaway near the equator, the true extinction of some Paleozoic radiolarian groups took place at the middle of the Early Triassic, immediately after the Smithian, rather than during the Permian–Triassic crisis.