Stelladinium bifurcatum n. sp., a distinctive extant thermophilic heterotrophic dinoflagellate cyst from the late Quaternary of the eastern Pacific and east equatorial Atlantic oceans

Stelladinium bifurcatum n. sp. is a large and distinctive brown heterotrophic dinoflagellate cyst recorded from Upper Pleistocene through modern sediments of the eastern Pacific, modern sediments of the western Bay of Bengal and sediment traps from the South China Sea, and Upper Pleistocene through Middle Holocene deposits of the east equatorial Atlantic. It is distinguished by prominent apical and antapical horns, numerous long processes distributed along the cingulum, tips of horns and processes that are characteristically solid or thickened and taper to points, a prominent flagellar scar, and an archeopyle formed by the second anterior intercalary plate with the operculum adnate along the right lateral margin. Stelladinium bifurcatum has been recorded in the literature under several names including “Stelladinium reidii” and the cyst of Protoperidinium stellatum from which it differs in having abundant cingular processes, at least one of which usually has a strongly divergent bifurcation. Re-examination of published records shows Stelladinium bifurcatum to have a tropical–subtropical neritic distribution in modern sediments of the eastern Pacific margin and to be associated with high biological productivity. Similarly in Pleistocene–Holocene sediments off west equatorial Africa, Stelladinium bifurcatum is linked to elevated sea-surface temperatures during the last deglaciation, and it serves as a marker of river discharge associated with an increase in monsoonal dynamics at this time.