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The Kingdom Protista or Protoctista is one of the commonly recognized biological kingdoms, including all the eukaryotes except for the plantGreen algae land plants (embryophytes non-vascular embryophytes Hepatophyta liverworts Anthocerophyta hornworts Bryophyta mosses vascular plants (tracheophytes seedless vascular plants Lycopodiophyta clubmosses Equisetophyta horsetails Pteridophyta "true"s, fungiChytridiomycota Zygomycota Ascomycota Basidiomycota The Fungi (singular: fungus are a large group of organisms ranked as a kingdom within the Domain Eukaryota. Included are the conspicuous mushrooms, but also many microscopic forms such as molds and yeast, animalSubkingdom Parazoa Porifera (sponges) Subkingdom " Agnotozoa" Placozoa Orthonectida Rhombozoa Subkingdom Metazoa "Radiata" Cnidaria Ctenophora (comb jellies) Bilateria Protostomia Acoelomorpha Platyhelminthes (flatworms) Nemertina (ribbon worms) Gastrotris, and sometimes other groups which are treated in separate kingdoms. A few forms are multicellular, for instance the brownDictyotales Desmerestiales Fucales Laminariales (kelps) etc. The brown algae are a large group of multicellular algae, including various sorts of seaweed. Their distinctive greenish-brown color comes from the pigment fucoxanthin. Well-known members includ and red algae. The vast majority, though, comprise the single-celled organisms, and are typically only 0.01-0.5 mm in size, usually too small to be seen without a microscopeA microscope is an instrument for viewing objects that are too small to be seen by the naked or unaided eye. The science of investigating small objects using such an instrument is called microscopy, and the term microscopic means minute or very small, not. Protists are ubiquitous throughout aqueous environments and the soil, commonly surviving dry periods in the form of cysts; a few are important parasites.
Traditionally protists have been divided into:
- PlantGreen algae land plants (embryophytes non-vascular embryophytes Hepatophyta liverworts Anthocerophyta hornworts Bryophyta mosses vascular plants (tracheophytes seedless vascular plants Lycopodiophyta clubmosses Equisetophyta horsetails Pteridophyta "true"-like forms that have chloroplasts, the algae:
- Fungus-like forms:
- Animal-like forms, the protozoa, generally divided on the basis of morphology and locomotion into:
In early classifications the protozoa were considered a phylum of animals, and the algae and slime moulds were placed among several divisions of plants. Many forms were classified under both kingdoms and researched by zoologists and botanists alike. Eventually the kingdom Protista was created to house these forms, with the classes of protozoa (corresponding roughly to the above) being promoted to phyla. Except for the ciliates and water moulds, however, all the above groups are polyphyletic and frequently overlapping. Further, the protists themselves are understood to be paraphyletic to the other eukaryotic kingdoms.
More recently attempts have been made to divide protists into more genuine groups on the basis of ultrastructural, chemical, and genetic features. In newer classification systems these are often treated as separate kingdoms. However, there are still many different lines of protists whose relationships are not understood. Many scientists now consider the various protist clades as direct subgroups of the eukaryotes, with the admission that we do not yet know enough about them to properly arrange them into a hierarchy. A few major groups are listed at right; others are described under the pages linked to above.
Protista
