Atlanticodinium striaticonulum n. gen., n. sp., a widespread extant dinoflagellate cyst from the late Cenozoic, and its comparison with Atlanticodinium janduchenei (Head et al., 1989) n. comb

Abstract Atlanticodinium n. gen. accommodates small- to medium-sized proximate dinoflagellate cysts with a spherical or subspherical central body having a nonfibrous wall with a smooth to finely ornamented surface bearing numerous, short, hollow, unbranched, nontabular, nonfibrous processes. The archeopyle is precingular, its margins having well defined angles. Atlanticodinium striaticonulum n. gen., n. sp. has a IP archeopyle, and distinctive short, distally closed processes with internal striations. This species has a confirmed Lower Pleistocene record, possibly extending to at least upper Lower Pliocene, and occurs widely in modern marine sediments. Atlanticodinium janduchenei (Head et al. 1989) n. comb., here reassigned from the genus Operculodinium Wall et al., 1977, has smooth-shafted processes that can be distally open or closed, as confirmed by re-examination of the holotype and paratype from the Upper Miocene of the Labrador Sea. Atlanticodinium janduchenei has a reported stratigraphic range of Lower Miocene to Lower Pleistocene, but this requires reevaluating. Atlanticodinium striaticonulum has been widely mistaken for Atlanticodinium janduchenei in modern sediments. Atlanticodinium striaticonulum has a tropical to temperate modern distribution, and is particularly associated with offshore to oceanic settings where conditions are oligotrophic.