Definition: A kingdom of eukaryotes incorporating the algae and the protozoans that comprise the presumed ancestral stocks of the fungi, plant, and animal kingdoms; they lack the developmental pattern stemming from a blastula, typical of animals, the pattern of embryo development typical of plants, and development from spores as in the fungi. Included in Protoctista are the nucleated algae and seaweeds, the flagellated water molds, slime molds, and slime nets, and the protozoa; unicellular, colonial, and multicellular organisms are included, but the complex development of tissues and organs of plants and animals is absent. The term Protoctista replaces the term Protista, which connotes single-celled or acellular organisms, whereas the basal preplant (Protophyta) and preanimal (Protozoa) assemblages incorporated in Protoctista include many multicellular forms, because multicellularity appears to have evolved independently a number of times within these primitive groups.
[G. prōtos, the first, + ktizō, to establish]
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