@article{skelton_burkholder_parrow_2008, title={AXENIC CULTIVATION OF THE HETEROTROPHIC DINOFLAGELLATE PFIESTERIA SHUMWAYAE AND OBSERVATIONS ON FEEDING BEHAVIOR}, volume={44}, ISSN={["1529-8817"]}, DOI={10.1111/j.1529-8817.2008.00601.x}, abstractNote={ Pfiesteria shumwayae Glasgow et J. M. Burkh. [=Pseudopfiesteria shumwayae (Glasgow et J. M. Burkh.) Litaker, Steid., P. L. Mason, Shields et P. A. Tester] is a heterotrophic dinoflagellate commonly found in temperate, estuarine waters. P. shumwayae can feed on other protists, fish, and invertebrates, but research on the biochemical requirements of this species has been restricted by the lack of axenic cultures. An undefined, biphasic culture medium was formulated that supported the axenic growth of two of three strains of P. shumwayae. The medium contained chicken egg yolk as a major component. Successful growth depended on the method used to sterilize the medium, and maximum cell yields (104 · mL−1) were similar to those attained in previous research when P. shumwayae was cultured with living fish or microalgae. Additionally, P. shumwayae flagellate cells ingested particles present in the biphasic medium, allowing detailed observations of feeding behavior. This research is an initial step toward a chemically defined axenic culture medium and determination of P. shumwayae metabolic requirements.}, number={6}, journal={JOURNAL OF PHYCOLOGY}, author={Skelton, Hayley M. and Burkholder, JoAnn M. and Parrow, Matthew W.}, year={2008}, month={Dec}, pages={1614–1624} }
 @misc{burkholder_g. m._g._a._h. a._d. w._m. w._m. j._p. v._e. h._et al._2007, title={Phytoplankton and bacterial assemblages in ballast water of US military ships as a function of port of origin, voyage time, and ocean exchange practices}, volume={6}, number={4}, journal={Harmful Algae}, author={Burkholder, J. M. and G. M., Melia and G., Cohen and A., Bowers and H. A., Oldach and D. W., Parrow and M. W., Sullivan and M. J., Zimba and P. V., Allen and E. H., Kinder and et al.}, year={2007}, pages={486–518} }
 @article{glibert_burkholder_parrow_lewitus_gustafson_2006, title={Direct uptake of nitrogen by Pfiesteria piscicida and Pfiesteria shumwayae, and nitrogen nutritional preferences}, volume={5}, ISSN={["1878-1470"]}, DOI={10.1016/j.hal.2006.04.009}, abstractNote={The rates of uptake of a range of forms of nitrogenous nutrients were measured in cultures of Pfiesteria piscicida and Pfiesteria shumwayae maintained at varying physiological states. The measured rates of dissolved N uptake under some conditions approached the rates of N uptake that are achieved through phagotrophy. Rates of dissolved N uptake by P. piscicida contributed <10% of the cellular N of flagellated cells feeding on algae, but were equal to or greater than phagotrophic N acquisition in cells recently removed from fish cultures. Specific N uptake rates (V, h−1) were higher for cells that were maintained on algal prey for long periods (months) than those that were grown with live fish. However, rates of N uptake on a cellular basis for cells grown on or recently removed from fish were comparable to those maintained on algal prey, likely reflecting differences in the sizes of cells of different physiological condition. Preferences for form of N generally followed a decreasing trend of amino acids > urea > NH4+ > NO3−. Nitrate consistently was not a preferred form of N. Although Pfiesteria spp. are often found in eutrophic environments, the relationship between Pfiesteria spp. and nutrient availability is likely to be primarily indirect, mediated through the production of various prey on which Pfiesteria spp. feed. These findings also confirm, however, that when dissolved N concentrations are elevated, they can contribute to the supplemental nutrition of these cells, and thus may provide a significant source of N to Pfiesteria spp. in nature.}, number={4}, journal={HARMFUL ALGAE}, author={Glibert, Patricia M. and Burkholder, JoAnn M. and Parrow, Matthew W. and Lewitus, Alan J. and Gustafson, Daniel E.}, year={2006}, month={Sep}, pages={380–394} }
 @article{kremp_parrow_2006, title={Evidence for asexual resting cysts in the life cycle of the marine peridinoid dinoflagellate, Scrippsiella hangoei}, volume={42}, ISSN={["1529-8817"]}, DOI={10.1111/j.1529-8817.2006.00205.x}, abstractNote={Scrippsiella hangoei(Schiller) Larsen is a peridinoid dinoflagellate that grows during winter and spring in the Baltic Sea. In culture this species formed round, smooth cysts when strains were mixed, indicating heterothallic sexuality and hypnozygote production. However, cysts of the same morphology were also formed in clonal strains exposed to slightly elevated temperature. To better understand the role of cysts in the life cycle ofS. hangoei, cyst formation and dormancy were examined in culture experiments and the cellular DNA content of flagellate cells and cysts was compared in clonal and mixed strains using flow cytometry.S. hangoeiexhibited a high rate of cyst formation in culture. Cysts produced in both clonal and mixed strain cultures were thick‐walled and underwent a dormancy period of 4 months before germinating. TheS. hangoeiflagellate cell population DNA distributions consisted of 1C, intermediate, and 2C DNA, indicative of respective eukaryotic cell cycle phases G1, S, and G2M. The majority (>95%) of cysts had a measured DNA content equivalent to the lower 1C DNA value, indicating a haploid nuclear phase and an asexual mode of cyst formation. A small percentage (<5%) of cysts produced in the mixed strain culture had 2C DNA, and thus could have been diploid zygotes. These findings represent the first measurements of dinoflagellate resting cyst DNA content, and provide the first quantitative evidence for dinoflagellate asexual resting cysts. Asexual resting cysts may be a more common feature of dinoflagellate life cycles than previously thought.}, number={2}, journal={JOURNAL OF PHYCOLOGY}, author={Kremp, A and Parrow, MW}, year={2006}, month={Apr}, pages={400–409} }
 @article{lewitus_wetz_willis_burkholder_parrow_glasgow_2006, title={Grazing activity of Pfiesteria piscicida (Dinophyceae) and susceptibility to ciliate predation vary with toxicity status}, volume={5}, ISSN={["1878-1470"]}, DOI={10.1016/j.hal.2006.04.012}, abstractNote={Variability has been reported in the toxicity potential of Pfiesteria piscicida that is partly a function of the history of exposure to live fish. Grazing properties of P. piscicida and its susceptibility to ciliate predation were compared in three functional types or toxicity states of this species: actively toxic cultures, cultures with temporary loss of demonstrable toxicity, and cultures with no demonstrable toxicity. Pronounced differences in predator–prey interactions were found between actively toxic cultures and cultures with reduced toxicity. When grown with Rhodomonas sp. (Cryptophyceae) prey, specific growth rates were relatively low in actively toxic cultures under both relatively high and low irradiances. In the cultures with reduced toxicity, prey chloroplast material was apparent in nearly 100% of dinoflagellate cells 3 h after feeding, while chloroplast inclusions were found in <40% of actively toxic cells for ≤16 h (high light) and ≤23 h (low light). These results suggest a relatively high reliance on phagotrophic carbon assimilation and more rapid response to algal prey availability in Pfiesteria cells with lower toxicity. Grazing by two euplotid benthic ciliates (Euplotes vannus and E. woodruffi) on P. piscicida also varied among functional types. Grazing on actively toxic P. piscicida cells did not occur, whereas net positive ingestion rates were calculated for the other prey cultures. These results support concurrent experimental findings that a natural assemblage of microzooplankton displayed lower grazing potential on actively toxic P. piscicida than on cultures with reduced toxicity. In summary, pronounced differences in trophic interactions were found between actively toxic cultures and those with reduced or undetectable toxicity, providing additional evidence of the importance of cellular toxicity in the trophic ecology of Pfiesteria.}, number={4}, journal={HARMFUL ALGAE}, author={Lewitus, Alan J. and Wetz, Michael S. and Willis, Bonnie M. and Burkholder, JoAnn M. and Parrow, Matthew W. and Glasgow, Howard B.}, year={2006}, month={Sep}, pages={427–434} }
 @article{skelton_parrow_burkholder_2006, title={Phosphatase activity in the heterotrophic dinoflagellate Pfiesteria shumwayae}, volume={5}, ISSN={["1878-1470"]}, DOI={10.1016/j.hal.2006.04.010}, abstractNote={The ELF-97 phosphatase substrate was used to examine phosphatase activity in four strains of the estuarine heterotrophic dinoflagellate, Pfiesteria shumwayae. Acid and alkaline phosphatase activities also were evaluated at different pH values using bulk colorimetric methods. Intracellular phosphatase activity was demonstrated in P. shumwayae cells that were actively feeding on a fish cell line and in food limited cells that had not fed on fish cells for 3 days. All strains, whether actively feeding or food limited showed similar phosphatase activities. P. shumwayae cells feeding on fish cells showed ELF-97 activity near, or surrounding, the food vacuole. Relatively small, spherical ELF-97 deposits were also observed in the cytoplasm and sometimes near the plasma membrane. ELF-97 fluorescence was highly variable among cells, likely reflecting different stages in digestion and related metabolic processes. The location of enzyme activity and supporting colorimetric measurements suggest that, as in other heterotrophic protists, acid phosphatases predominate in P. shumwayae and have a general catabolic function.}, number={4}, journal={HARMFUL ALGAE}, author={Skelton, Hayley M. and Parrow, Matthew W. and Burkholder, JoAnn M.}, year={2006}, month={Sep}, pages={395–406} }
 @article{marshall_hargraves_burkholder_parrow_elbraechter_allen_knowlton_rublee_hynes_egerton_et al._2006, title={Taxonomy of Pfiesteria (Dinophyceae)}, volume={5}, ISSN={["1878-1470"]}, DOI={10.1016/j.hal.2006.05.001}, abstractNote={The dinoflagellate species originally described as Pfiesteria shumwayae Glasgow et Burkholder, recently transferred to a new genus, Pseudopfiesteria Litaker et al., is reclassified into the redefined genus Pfiesteria Steidinger et Burkholder, as Pfiesteria shumwayae within the order Peridiniales. This change is based upon consideration of a compilation of previous and new morphological analyses and molecular phylogenetic analyses. Morphological analysis with scanning and transmission electron microscopy supports previous findings except in the sulcal area. In the cells examined, the sulcus is partly concealed by the peduncle cover plate (p.c.), which originates at the right side of the sulcus along the left side of the 6c and 5‴ plates. The fine structure of the p.c. appears similar to that of other thecal plates. The 1″ plate can also extend slightly over the sulcus. Transmission electron microscopy revealed that Pfiesteria shumwayae can have at least six sulcal plates; the number remains uncertain and may vary. The sulcal plates of this small, delicately thecate species have not been clearly discerned by scanning electron microscopy of membrane-stripped and/or suture-swollen cells. The Kofoidian thecal plate formula for the genus Pfiesteria is Po, cp, X, 4′, la, 5–6″, 6c, p.c., ?s, 5‴, 0p, 2‴′. The monophyletic grouping of “pfiesteria-like” taxa within the order Peridiniales, as well as the grouping of Pfiesteria piscicida and Pfiesteria shumwayae within the same genus, is also supported by the preponderance of previous molecular evidence, and by the phylogenetic trees contributed in the present analysis. Pfiesteria appears to be closely related to as-yet informally described cryptoperidiniopsoids and calcareous dinoflagellates such as Thoracosphaera; thus, the family classification requires revision that is beyond the scope of this study.}, number={5}, journal={HARMFUL ALGAE}, author={Marshall, Harold G. and Hargraves, Paul E. and Burkholder, JoAnn M. and Parrow, Matthew W. and Elbraechter, Malte and Allen, Elle H. and Knowlton, Valerie M. and Rublee, Parke A. and Hynes, Wayne L. and Egerton, Todd A. and et al.}, year={2006}, month={Oct}, pages={481–496} }
 @article{parrow_elbraechter_krause_burkholder_deamer_htyte_allen_2006, title={The taxonomy and growth of a Crypthecodinium species (Dinophyceae) isolated from a brackish-water fish aquarium}, volume={28}, ISSN={["1814-232X"]}, DOI={10.2989/18142320609504145}, abstractNote={An unidentified heterotrophic dinoflagellate found growing in abundance in a brackish-water fish aquarium was isolated and serially cultivated using a fish cell line as the food source. Prominent characteristics of this dinoflagellate included a cingulum that did not fully encircle the motile cell, cell division in non-motile cysts, and a theca composed of thin but structured plates. Morphological analysis of flagellate cells by scanning electron microscopy revealed a Kofoid thecal plate tabulation of 4', 4a, 4", 'X', 5 or 6c, ?s, 5"', 1p, 1"", most consistent with the original description of Crypthecodinium setense Biecheler. This Crypthecodinium species exhibited a high maximum division rate (3.2 divisions day−1) and cell yield (>106 cells ml−1) when fed cultured fish cells. Small sub-unit rDNA phylogenetic analyses supported relatedness with a previously studied Crypthecodinium-like dinoflagellate, but a significant difference in aligned gene sequences was found. This study provides the first clear demonstration of the plate tabulation of a Crypthecodinium species since the original description over 60 years ago, allowing the original morphological conception of Crypthecodinium to be linked with molecular phylogenetic information.}, number={2}, journal={AFRICAN JOURNAL OF MARINE SCIENCE}, author={Parrow, M. W. and Elbraechter, M. and Krause, M. K. and Burkholder, J. M. and Deamer, N. J. and Htyte, N. and Allen, E. H.}, year={2006}, month={Sep}, pages={185–191} }
 @article{parrow_burkholder_deamer_ramsdell_2005, title={Contaminant-free cultivation of Pfiesteria shumwayae (Dinophyceae) on a fish cell line}, volume={39}, ISSN={["0948-3055"]}, DOI={10.3354/ame039097}, abstractNote={Geographically distinct strains of the heterotrophic dinoflagellate Pfiesteria shumwayae were cultivated on a fish cell line in the apparent absence of bacteria and other microbial conta- minants. Cultures were established with a high rate of success by inoculating single purified P. shumwayae cells into fish cell cultures containing a simple saltwater medium suitable for both cell types, and resulting isolates were serially cultivated on fish cells for months without visible signs of abnormality or reduced viability. P. shumwayae fed phagocytically on the fish cells and exhibited higher cell production than reported using other culturing methods. Compared to previous methods of studying the interaction between Pfiesteria spp. and fishes, this system enabled closer and more direct observation of the dinoflagellates and was also more economical and sustainable as a culturing method. The absence of bacteria and other contaminating microorganisms should facilitate important physiological and biochemical investigations. The methods used were inadequate for cultivating strains of P. piscicida, suggesting a possible difference in nutritional requirements between the 2 Pfiesteria species.}, number={1}, journal={AQUATIC MICROBIAL ECOLOGY}, author={Parrow, MW and Burkholder, JM and Deamer, NJ and Ramsdell, JS}, year={2005}, month={Apr}, pages={97–105} }
 @article{parrow_burkholder_2004, title={The sexual life cycles of Pfiesteria piscicida and cryptoperidiniopsoids (Dinophyceae)}, volume={40}, ISSN={["1529-8817"]}, DOI={10.1111/j.1529-8817.2004.03202.x}, abstractNote={Sexual life cycle events in Pfiesteria piscicida and cryptoperidiniopsoid heterotrophic dinoflagellates were determined by following the development of isolated gamete pairs in single‐drop microcultures with cryptophyte prey. Under these conditions, the observed sequence of zygote formation, development, and postzygotic divisions was similar in these dinoflagellates. Fusion of motile gamete pairs each produced a rapidly swimming uninucleate planozygote with two longitudinal flagella. Planozygotes enlarged as they fed repeatedly on cryptophytes. In <12 h in most cases, each planozygote formed a transparent‐walled nonmotile cell (cyst) with a single nucleus. Zygotic cysts did not exhibit dormancy under these conditions. In each taxon, dramatic swirling chromosome movements (nuclear cyclosis) were found in zygote nuclei before division. In P. piscicida, nuclear cyclosis occurred in the zygotic cyst or apparently earlier in the planozygote. In the cryptoperidiniopsoids, nuclear cyclosis occurred inthe zygotic cyst. After nuclear cyclosis, a single cell division occurred in P. piscicida and cryptoperidiniopsoid zygotic cysts, producing two offspring that emerged as biflagellated cells. These two flagellated cells typically swam for hours and fed on cryptophytes before encysting. A single cell division in these cysts produced two biflagellated offspring that also fed before encysting for further reproduction. This sequence of zygote development and postzygotic divisions typically was completed within 24 h and was confirmed in examples from different isolates of each taxon. Some aspects of the P. piscicida sexual life cycle determined here differed from previous reports.}, number={4}, journal={JOURNAL OF PHYCOLOGY}, author={Parrow, MW and Burkholder, JM}, year={2004}, month={Aug}, pages={664–673} }
 @misc{parrow_burkholder_2003, title={Estuarine heterotrophic cryptoperidiniopsoids (Dinophyceae): Life cycle and culture studies}, volume={39}, ISSN={["1529-8817"]}, DOI={10.1046/j.1529-8817.2003.02146.x}, abstractNote={Cryptoperidiniopsoids are an unclassified group of delicately thecate heterotrophic dinoflagellates known to be common in eastern U.S. estuarine waters. Over the past 10 years cryptoperidiniopsoids were isolated from different geographical regions and cultured with cryptophyte algal prey. In the seven clonal isolates examined, reproduction was strongly linked to the availability of prey cells. The dinoflagellates phagocytized the contents of prey cells through a tube‐like peduncle, similarly as close relatives of Pfiesteria spp. and several other heterotrophic species. Cell division occurred while encysted, most commonly yielding two biflagellated offspring. Abundant fusing gametes, phagotrophic planozygotes, and cysts with a pronounced nuclear cyclosis characterized persistent sexuality. Cysts with nuclear cyclosis produced two flagellated offspring cells. The resistance of reproductive cysts to antimicrobial treatments was examined, and a simple high‐yield technique was developed for population synchronization while ridding the dinoflagellates of most contaminating vacuolar prey DNA and external contaminants. The DNA content and population DNA profiles of synchronously excysted cryptoperidiniopsoids from different isolates were measured using flow cytometry and were related to the life history of these and other dinoflagellates. Cryptophyte‐fed cultures with versus without extracellular bacteria were compared, and bacteria apparently promoted cryptoperidiniopsoid feeding and growth. Externally bacteria‐free dinoflagellates were cultured in media enriched with dissolved organic nutrients, and nutritional benefit may have occurred in some treatments. The potential for mixotrophic nutrition from maintenance of cryptophyte chloroplasts was examined using flow cytometrically sorted cells, but evidence of kleptoplastidy was not found in these isolates under the conditions imposed.}, number={4}, journal={JOURNAL OF PHYCOLOGY}, author={Parrow, MW and Burkholder, JM}, year={2003}, month={Aug}, pages={678–696} }
 @article{parrow_burkholder_2003, title={Reproduction and sexuality in Pfiesteria shumwayae (Dinophyceae)}, volume={39}, ISSN={["1529-8817"]}, DOI={10.1046/j.1529-8817.2003.03057.x}, abstractNote={ Pfiesteria shumwayae is a heterotrophic dinoflagellate with a widespread distribution in temperate‐subtropical estuarine waters. In this study, five clonal isolates from the eastern coast of North America, one from New Zealand, and a mixed composite of clones were cultured in aquaria and fed live fish. Division, sexuality, and phagotrophic feeding on fish were studied by LM, SEM, and flow cytometry. The development of reproductive cysts isolated from aquaria was followed. Synchronously excysted flagellate populations were examined for sexuality and then for feeding behavior and reproduction when given larval fish. Reproductive cysts varied in size and underwent protoplast division(s), most commonly producing two to eight biflagellated offspring. Fusing gametes, resulting planozygotes, and nuclear cyclosis were documented as evidence of sexuality. Gametes emerged from cysts, and fusions were approximately isogamous. Resulting planozygotes had two longitudinal flagella and one transverse flagellum and apparently fed before encysting. Distinct and lengthy chromosome movements (nuclear cyclosis) occurred in presumed zygotic cysts before nuclear division(s). These cysts did not exhibit dormancy in growing cultures and produced two or four biflagellated offspring. Flagellated cells fed on surficial fish tissues and then encysted for reproduction. Stages indicating a completed sexual cycle (fusion, planozygotes, and nuclear cyclosis) were uncommon or absent in clonal cultures but were relatively abundant in the mixed clone culture. Self‐sterility factors apparently influenced sexuality. Starved populations formed quiescent cysts that released swimming cells when food was provided. Pfiesteria shumwayae was similar in reproduction and sexuality to closely related species.}, number={4}, journal={JOURNAL OF PHYCOLOGY}, author={Parrow, MW and Burkholder, JM}, year={2003}, month={Aug}, pages={697–711} }
 @article{parrow_burkholder_2002, title={Flow cytometric determination of zoospore DNA content and population DNA distribution in cultured Pfiesteria spp. (Pyrrhophyta)}, volume={267}, ISSN={["0022-0981"]}, DOI={10.1016/S0022-0981(01)00343-4}, abstractNote={The relative cellular DNA content from 23 different clonal cultures of Pfiesteria spp. zoospores was determined using a DNA fluorochrome and flow cytometry. Significant differences between Pfiesteria piscicida and P. shumwayae were detected, both in mean zoospore DNA content and population cell cycle DNA distribution. Intraspecific differences in DNA content were found between clonal zoospore cultures established from different geographical regions. Long-term cultures (years) of P. piscicida were available for testing, and a negative correlation was observed between zoospore DNA content and time in culture. Zoospore cell cycle-related DNA distributions were also markedly different between the two species in these clonal cultures. In most cultures tested, P. piscicida zoospores exhibited bimodal DNA flow histograms with G1-S-G2+M distributions, typical of eukaryotic asynchronously cycling cells. In contrast, cultures of P. shumwayae zoospores exhibited one DNA peak distribution, indicative of synchronized cells. The data are consistent with the hypothesis that P. shumwayae zoospores are interphasic cells, and mitosis in zoospore cultures of this species predominantly occurs as benthic or adherent non-motile division cysts. Light microscopy observations of the nuclear condition of electrostatically sorted zoospores of each Pfiesteria species also support this hypothesis. If highly conserved, this disparity in modes of vegetative reproduction would ramify the population dynamics of the two Pfiesteria species.}, number={1}, journal={JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY}, author={Parrow, MW and Burkholder, JA}, year={2002}, month={Jan}, pages={35–51} }
 @article{parrow_burkholder_2002, title={Flow cytometric determination of zoospore DNA content and population DNA distribution in cultured Pfiesteria spp. (Pyrrhophyta) (vol 267, pg 35, 2002)}, volume={268}, ISSN={["0022-0981"]}, DOI={10.1016/S0022-0981(02)00018-7}, number={2}, journal={JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY}, author={Parrow, MW and Burkholder, JM}, year={2002}, month={Feb}, pages={261–261} }
 @article{stoecker_parrow_burkholder_glasgow_2002, title={Grazing by microzooplankton on Pfiesteria piscicida cultures with different histories of toxicity}, volume={28}, ISSN={["1616-1564"]}, DOI={10.3354/ame028079}, abstractNote={Susceptibility of actively toxic (TOX-A) zoospores, temporarily non-toxic (TOX-B) zoospores, and zoospores non-inducible to toxicity (NON-IND) of Pfiesteria piscicida to microzoo- plankton grazing was compared in a laboratory experiment. Zoospores from all cultures were ingested by microzooplankton, but community grazing coefficients for TOX-A were < 20% of those for TOX-B or NON-IND zoospores in 6 h incubations. Tintinnids and strobilidiid ciliates that fed on P. piscicida declined in incubations containing TOX-A zoospores. There was no decline in a strom- bidiid ciliate or heterotrophic dinoflagellate populations that fed on TOX-A zoospores. These data suggest that, although microzooplankton grazing on non-toxic zoospores can be a significant source of mortality to planktonic populations of P. piscicida, grazing on toxic or very recently toxic zoospores is relatively low.}, number={1}, journal={AQUATIC MICROBIAL ECOLOGY}, author={Stoecker, DK and Parrow, MW and Burkholder, JM and Glasgow, HB}, year={2002}, month={May}, pages={79–85} }
 @article{parrow_burkholder_deamer_zhang_2002, title={Vegetative and sexual reproduction in Pfiesteria spp. (Dinophyceae) cultured with algal prey, and inferences for their classification.}, volume={1}, DOI={10.1016/s1568-9883(02)00009-4}, abstractNote={Algal-fed clonal zoospore cultures of Pfiesteria piscicida and Pfiesteria shumwayae enabled description of certain conserved morphological and reproductive features. Common modes of reproduction (especially via division cysts) were documented in herbivorous P. piscicida and P. shumwayae using cultures fed algal prey, together with supporting photography and flow cytometric DNA measurements. Other cysts were characterized such as vacuolate cysts in starved P. piscicida cultures and temporary cysts in both species fed algal prey. This study also represents the first report of sexual reproduction in Pfiesteria spp. cultures fed algal prey rather than live fish; the first report of a technique for cell cycle synchronization for these heterotrophic dinoflagellates; and the first information on storage products of cells released from Pfiesteria reproductive cysts. Sexual reproduction in algal-fed P. piscicida clonal cultures was evidenced by fusing gametes, cells with two longitudinal flagella, and nuclear cyclosis. Both isogamous and anisogamous fusions were observed, and resulting cells with two trailing flagella (i.e., planozygotes and planomeiocytes) sometimes comprised ≥50% of the flagellated cells. These cells continued feeding activity and eventually (hours) lost their flagella and formed cysts. Nuclear cyclosis and a subsequent cell division were observed in thin-walled reproductive cysts prior to release of two flagellated cells. One gamete fusion event was also documented in 1 of 20 algal-fed clones of P. shumwayae, with an aplanozygote as the product. We obtained high cell synchrony (≥90% 1C) in the tested cultures using our preferential lysis technique and tracked the decline in lipid content of excysted zoospore populations over time. The data from this study were considered together with previous research to gain insights about relationships between Pfiesteria spp. and other heterotrophic dinoflagellates. Pfiesteria spp. should be regarded as free-living predators rather than parasites because they are prey generalists without demonstrated “host” specificity and their flagellated feeding stages are not morphologically distinct from swimming stages. Although they originally were placed within the Dinamoebales because amoebae can predominate, this study as well as other published research consistently has shown that the dominant stage varies depending on culture conditions, prey type/availability and strains. The peridinoid plate structure of each Pfiesteria species, which thus far has been conserved across culture conditions and strains, supports placement of Pfiesteria spp. within the Peridiniales. At the species level, plate structure (differing by one precingular plate) and molecular data (18S rDNA) indicate that the two Pfiesteria spp. are closely related in comparison to species grouped within other genera.}, number={1}, journal={Harmful Algae}, author={Parrow, M. and Burkholder, J. M. and Deamer, N. J. and Zhang, C.}, year={2002}, pages={5–33} }