pro·toc·tist

(prə-tōk′tĭst)

Any of various eukaryotic organisms belonging to the kingdom Protoctista in some classification systems. Protoctists include unicellular and multicellular organisms that are not fungi, plants, or animals. They are usually now referred to as protists.

[From New Latin Prōtoctista, kingdom name : Greek prōto-, proto- + Greek ktistos, produced, created (from ktizein, to create, establish; see tkei- in Indo-European roots).]

American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

protoctist

(prəʊˈtɒktɪst)

(Biology) (in modern biological classifications) any unicellular or simple multicellular organism belonging to the kingdom Protoctista, which includes protozoans, algae, and slime moulds

[C19: from New Latin protoctista, perhaps from Greek prōtotokos first born]

Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014

pro·toc·tist

(prə-tŏk′tĭst)

See protist.

The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

ThesaurusAntonymsRelated WordsSynonymsLegend:

Noun

protoctist - any of the unicellular protists

microorganism, micro-organism - any organism of microscopic size

kingdom Protoctista, Protoctista - in most modern classifications, replacement for the Protista; includes: Protozoa; Euglenophyta; Chlorophyta; Cryptophyta; Heterokontophyta; Rhodophyta; unicellular protists and their descendant multicellular organisms: regarded as distinct from plants and animals

protozoan, protozoon - any of diverse minute acellular or unicellular organisms usually nonphotosynthetic

alga, algae - primitive chlorophyll-containing mainly aquatic eukaryotic organisms lacking true stems and roots and leaves

Mentioned in

References in periodicals archive

The karyomastigont, an organellar system that includes the nucleus, the nuclear connector, and kinetosome-centrioles in many protoctist and animal cells, is a conspicuous component of the cytoskeleton.

Spirochete attachment ultrastructure: implications for the origin and evolution of cilia

The Protoctist Kingdom (0761418180), Reptile Class (0761418202), Insect Class (0761418199), Flowering Plant Kingdom (0761418172) and Primate Order (0761-418164) by Stefoff each survey kingdoms and species, classification methods, physical traits, adaptations, and life cycles.

Marshall Cavendish

Nearly one in five species in the fungal kingdom forms a composite with an alga, which is from the protist, or protoctist, kingdom.

Yikes! The Lichens Went Flying

Kala-azar, or visceral leishmaniasis, is caused by the presence in the blood and some organs, such as liver, spleen, and bone marrow, of the parasitic kinetoplastid protoctist Leishmania donovani, which is transmitted by the bite of a sandfly Phlebotomus.

3 Humans in the monsoon forests

In particular, the role of the microheterotrophs, protoctist microorganisms that feed on microalgae and bacteria, may be of great importance in the food webs of the Antarctic Ocean.

5 The Antarctic dominion

The second type of sex is hypersex, characteristic of the protoctists; microorganisms that comprise one of the five kingdoms of living organisms (i.e., protoctista; plantae, animalia, fungi, and bacteria).

Chapter 2: Life, reproduction, and sex

As Case noted, attempted reconciliation of five Kingdoms (Bacteria, Protoctists, Animals, Plants, Fungi) with three Domains (Bacteria, Archaea, Eucarya) resulted in a "compromise" of six kingdoms (Archaebacteria, Eubacteria, Protista, Fungi, Plantae, Animalia)--an outcome that does not fully represent the intent of either the five-kingdom or three-domain system.

Merging kingdoms and domains

The five kingdoms system identifies five categories of organisms as rational kingdom divisions: bacteria (the prokaryotic or nucleus-lacking microbes), protoctists (algae, slime molds, and other nucleated eukaryotic organisms formed by symbiosis from bacteria), fungi (mushrooms, molds, and yeasts, all of which reproduce by spores), plants (organisms that develop from spores and embryos retained by the mother's tissue), and animals (organisms that develop from eggs fertilized by sperm).

Mapping the Geography of Symbiosis

Class 2 Foraminifera (Reticulopodate with Shell, Foraminiferans, Forams) Phylum 4 Xenophyophora (Large Deep-Sea Benthic Protoctists)

Appendices

He rejoices in turns of phrase like "protoctists pop out of their protective cysts" and "the great mycelial clot beneath a toadstool"; of the burning of fossil fuels he remarks that the carbon released in the process "floods the carbon cycle, as if the dead should arise from their graves and flood the job market." His assessment of current agricultural practices is as memorable as it is severe:

Scarcity and Plenitude: Thoughts on Some Recent Jewish Books

protoctists, and bacteria], animals may be defined as multicellular,

Sortal essentialism and the potentiality principle

For decades, most biologists accepted the classification of all life into five kingdoms: Bacteria (or Monera), Protoctists (protists and their macroscopic relatives), Animals, Plants, and Fungi (Figure 1).

Teaching taxonomy: how many Kingdoms?