The classic portrayal of plankton is dominated by phytoplanktonic primary producersand zooplanktonic secondary producers. In reality, many if not most planktontraditionally labelled as phytoplankton or microzooplankton should be identifiedas mixotrophs, contributing to both primary and secondary production. Mixotrophicprotists (i.e. single-celled eukaryotes that perform photosynthesis and grazeon particles) do not represent a minor component of the plankton, as some formof inferior representatives of the past evolution of protists; they represent a majorcomponent of the extant protist plankton, and one which could become moredominant with climate change. The implications for this mistaken identification, ofthe incorrect labelling of mixotrophs as “phytoplankton” or “microzooplankton”,are great. It extends from the (mis)use of photopigments as indicators of primaryproduction performed by strict photoautotrophs rather than also (co)locating mixotrophicactivity, through to the inadequacy of plankton functional type descriptionsin models (noting that mixotrophic production in the individual organism is not asimple sum of phototrophy and heterotrophy). We propose that mixotrophy shouldbe recognized as a major contributor to plankton dynamics, with due effortexpended in field and laboratory studies, and should no longer be side-lined inconceptual food webs or in mathematical models.