Among descriptions of field material, Esoptrodinium/Bernardinium populations or individual cells were described as having distinct yellow-green chloroplasts (Thompson 1951, Bicudo and Skvortzov 1970, Javornický 1997), lacking chloroplasts (Chodat 1924, Javornický 1962), or being indeterminate in this characteristic (Javornický 1962). The type species E. gemma was described as lacking distinct chloroplasts (Javornický 1997), as was the original type species B. bernardinense (Chodat phosphatase inhibitor library 1924), but the most recent taxonomic revision of this

group did not consider presence or absence of chloroplasts as a genus or species-level diacritical feature (Javornický 1997). In the first laboratory study of Esoptrodinium, Calado et al. (2006) demonstrated that their Portuguese isolate contained small yellow-green endogenous chloroplasts surrounded by a typical “peridinoid-type” triple membrane and also fed on chlorelloid microalgae, suggesting mixotrophic nutrition. Although the Esoptrodinium chloroplasts appeared structurally intact and were assumed to be functional, phototrophy was not determined and the authors suggested based on qualitative observations

that phagotrophy may have been the primary mode of nutrition in this isolate (Calado et al. 2006). More recently, Fawcett and Parrow (2012) brought multiple isolates of Esoptrodinium-like dinoflagellates from different ponds in North Carolina, United AZD1208 Stated into clonal culture and determined that they, along with the previously sequenced isolate from Portugal (Calado et al. 2006), formed a multibranched but strongly supported monophyletic nuclear rDNA clade within the Tovelliaceae. All U.S. isolates were robustly phagotrophic on the cryptophyte microalga Cryptomonas ovata, and qualitatively

appeared to require such prey cells in order to be maintained in the laboratory. Of the six isolates reported by Fawcett and Parrow (2012), four possessed distinctly visible pale-green chloroplasts, one lacked visible chloroplasts entirely, and another contained “cryptic” chloroplasts that were so reduced in size and pigmentation Quinapyramine as to be nearly undetectable under LM; the latter two isolates were not monophyletic. Curiously, the isolate with apparent “cryptic,” highly reduced chloroplasts shared an identical nuclear rDNA phylotype (entire 18S-ITS1-5.8S-ITS2 region plus D1-D2 of 28S) with three isolates from different ponds that contained distinct, plainly visible chloroplasts. Observation of closely related Esoptrodinium isolates that differed in presence/absence of visible chloroplasts recalled earlier field descriptions of such variability, and suggested that independent plastid reduction had occurred in some lineages and/or that visible, pigmented chloroplasts could represent an unusually variable intraspecific allelic trait in this taxon (Fawcett and Parrow 2012).