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A protist (/ ˈ p r oʊ t ɪ s t / PROH-tist) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus.Protists do not form a natural group, or clade, but are a polyphyletic grouping of several independent clades that evolved from the last eukaryotic common ancestor.
Protists are distributed across all major groups of eukaryotes, including those that contain multicellular algae, green plants, animals, and fungi. If photosynthetic and fungal protists are distinguished from protozoa, they appear as shown in the phylogenetic tree of eukaryotic groups.
Marine protists are defined by their habitat as protists that live in marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. Life originated as marine single-celled prokaryotes (bacteria and archaea) and later evolved into more complex eukaryotes .
Many extant dinoflagellates are parasites (here defined as organisms that eat their prey from the inside, i.e. endoparasites, or that remain attached to their prey for longer periods of time, i.e. ectoparasites). They can parasitize animal or protist hosts.
Protistology is a scientific discipline devoted to the study of protists, a highly diverse group of eukaryotic organisms. All eukaryotes apart from animals, plants and fungi are considered protists. [1]
Protists include all eukaryotes that are not animals, plants, or fungi, resulting in great diversity between them. Algae are photosynthetic protists that can produce energy from light. Several types of protists use mycelium similar to those of fungi. Protozoa are heterotrophic protists, and different protozoa seek nutrients in different ways.
Foraminifera (/ f ə ˌ r æ m ə ˈ n ɪ f ə r ə / fə-RAM-ə-NIH-fə-rə; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of Rhizarian protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly an external shell (called a "test") of diverse forms and materials.
Phytoplankton are very diverse, comprising photosynthesizing bacteria (cyanobacteria) and various unicellular protist groups (notably the diatoms). Many other organism groups formally named as phytoplankton, including coccolithophores and dinoflagellates, are now no longer included as they are not only phototrophic but can also eat. [6]