A Reconsideration of Living and Fossil Pyrophacus Stein, 1883 (Dinophyceae)1,2

SUMMARY Three previously described dinoflagellates (2 “varieties” and a “form”) that comprise the marine genus Pyrophacus Stein, 1883, are allocated, to 3 separate species for the first time after demonstration of appropriate discontinuities in their respective theca and cyst morphologies. Formerly they were called P. horologium Stein var. horologium, P. horologium var. steinii Schiller and, Pyrophacus Form B1 of Steidinger and Davis; they become P. horologium Stein, P. steinii (Schiller) nov. comb., and P. vancampoae (Rossignol) nov. comb. The newly discovered cyst stage of the latter is identical with the fossil dinoflagellate Tuberculodinium vancampoae (Rossignol) Wall, whose unusual morphology is reinterpreted to include an oblate body, 4 rows of intratabular tubercules, and a uniquely located hypotractal (posterior antapical) archeopyle. The outer wall of the newly discovered benthic encysted stage of P. horologium Stein is gelatinous and agglutinating in behavior and comparable with the amorphous “Kalyptra” that constitutes the outer wall layer of several extinct Mesozoic and Danian fossil dinoflagellates.