THE RECLASSIFICATION OF PFIESTERIA SHUMWAYAE (DINOPHYCEAE): PSEUDOPFIESTERIA, GEN. NOV. 1 R. Wayne Litaker 2 Center for Coastal Fisheries and Habitat Research, National Ocean Service, NOAA, 101 Pivers Island Rd., Beaufort, North Carolina 28516-9722, USA Karen A. Steidinger Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission, 100 Eighth Avenue SE, St. Petersburg, Florida 33701-5020, USA Patrice L. Mason Department of Environmental and Aquatic Animal Health, Virginia Institute of Marine Science, The College of William and Mary, P.O. Box 1346, Gloucester Point, Virginia 23062-1346, USA Jan H. Landsberg Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission, 100 Eighth Avenue SE, St. Petersburg, Florida 33701-5020, USA Jeffrey D. Shields, Kimberly S. Reece, Leonard W. Haas, Wolfgang K. Vogelbein Department of Environmental & Aquatic Animal Health, Virginia Institute of Marine Science, The College of William and Mary, P.O. Box 1346, Gloucester Point, Virginia 23062-1346, USA Mark W. Vandersea, Steven R. Kibler, and Patricia A. Tester Center for Coastal Fisheries and Habitat Research, National Ocean Service, NOAA, 101 Pivers Island Rd., Beaufort, North Carolina 28516-9722, USA Pfiesteria shumwayae Glasgow et Burkholder is assigned to a new genus Pseudopfiesteria gen. nov. Plate tabulation differences between Pfiesteria and Pseudopfiesteria gen. nov. as well as a maximum likelihood phylogenetic analysis based on rDNA se- quence data warrant creation of this new genus. The Kofoidian thecal plate formula for the new genus is Po, cp, X, 4 0 , 1a, 6 00 , 6c, PC, 5 þ s, 5 000 , 0p, 2 0000 . In addition to having six precingular plates, P. shum- wayae comb. nov. also has a distinctive diamond or rectangular-shaped anterior intercalary plate. Both Pfiesteria and Pseudopfiesteria gen. nov. are reas- signed to the order Peridiniales based on an apical pore complex (APC) with a canal (X) plate that con- tacts a symmetrical 1 0 , four to five sulcal plates, and the conservative hypothecal tabulation of 5 000 , 0p, and 2 0000 . These morphological characters and the life histories of Pfiesteria and Pseudopfiesteria are consistent with placement of both genera in the Peridiniales. Based on the plate tabulations for P . shumwayae, P. piscicida, and the closely related ‘‘cryptoperidiniopsoid’’ and ‘‘lucy’’ groups, the family Pfiesteriaceae is amended to include species with the following tabulation: 4-5 0 , 0-2a, 5-6 00 , 6c, PC, 5 þ s, 5 000 , 0p, and 2 0000 as well as an APC con- taining a pore plate (Po), a closing plate (cp), and an X plate; the tabulation is expanded to increase the number of sulcal plates and to include a new plate, the peduncle cover (PC) plate. Members of the fam- ily have typical dinoflagellate life cycles character- ized by a biflagellated free-living motile stage, a varying number of cyst stages, and the absence of multiple amoeboid stages. Key index words: evolution; Pfiesteria-like dinoflag- ellates; Pfiesteria shumwayae; Pseudopfiesteria; ribo- somal genes; taxonomy Abbreviations: APC, apical pore complex; ITS, in- ternal transcribed spacer; ML, maximum likeli- hood; LSU, large subunit; PC, peduncle cover plate; PLDs, Pfiesteria-like dinoflagellates; s.d.p., right (dexter) posterior sulcal plate; s.m., median sulcal plate; s.s, left (sinister) sulcal plate; SSU, small subunit Pfiesteria and Pfiesteria-like species are morphologi- cally similar thinly armored dinoflagellates with flagel- lated stages characterized by their distinct Kofoidian thecal plate formulae or plate tabulations. Currently, the plate formula of the genus Pfiesteria is characterized 1 Received 18 August 2004. Accepted 1 February 2005. Author for correspondence: e-mail Wayne.Litaker@noaa.gov. 643 J. Phycol. 41, 643–651 (2005) r 2005 Phycological Society of America DOI: 10.1111/j.1529-8817.2005.00075.x