Why are Ciliates Chromista I thought they were Protozoa

Under the life list, I was looking for some of my Hypotrich posts and species breakdown. So I went under Protozoa and I couldn’t find it. I decided to search for it and it was under “Kelp, Diatoms, and Allies”. Maybe I’m mistaken but I swear Hypotrich, Genus Frontonia, Genus Paramecium, etc are ciliated Protozoa. That is everything I am learning from college and personal research. Chromista contains “all protists whose plastids contain chlorophyll c,” Paramecium does not contain chlorophyll c just like Amoebozoa. My protozoa list only contains Phylum Amoebozoa, Euglenoids, and Slime Molds. Maybe I am mistaken and somehow Paramecium are Chromists but what I do know is that they are also Protozoans. So is it possible that Ciliates can be under both categories here? Can someone enlighten me as to why they categorize all Ciliates as Chromista on here? @loarie I noticed under the Taxonomy section then Taxonomy details it says “Created by loarie on November 16, 2018” so maybe you made a mistake on the taxonomy of Ciliates. :) I’m not sure how to change it but if you could that would be helpful.

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Historically, there have been multiple schemes for classifying “protists”, a term inconsistently applied to paraphyletic groups of taxa. The higher classifications for these that iNaturalist uses are based on the Catalogue of Life. This scheme (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4418965/) was based on literature and expert consensus, apparently. I don’t have any particular knowledge on the placement of ciliates but they are more closely related to dinoflagellates (chlorophyll-producing) than amoebas.


Many schemes don’t use Protozoa at all – the group is often broken into several kingdoms. I would expect that once researchers finally converge on a general taxonomy, iNat will break it up as well.


The “protists” have always been a place to put things that didn’t fit neatly into other kingdoms and until some of the more recent DNA techniques came around it was understood that very little could be done to sort it all out. The term “protozoa” came to mean single-celled protists and a current classification scheme has some of the traditional protozoans (ciliates and dinoflagellates) in a separate kingdom, Chromista.

The current taxonomic scheme for protists is a mess and that is the main takeaway you should get from that. However, it is getting better because whole DNA analysis is shedding light on relationships. But we are still scrambling a bit to understand why some of these groups are related based on physical characteristics. Despite any problems we are still having with the taxonomy the relationships that are being proposed are making a lot more sense. For instance, we are recognizing that different lines of protists are related to plants while others are to animals. It gives a much clearer picture of the evolution of those groups.

iNaturalist is using a particular scheme right now but this is likely to change as more consensus arises about the taxonomy. So currently we are in a sorting period and one of the better schemes that I have seen uses “supergroups” as an unofficial taxonomic category to help sort them. There are currently 4 supergroups recognized and I will list them below to show you how we think these different groups are associated. Keep in mind that all of these groupings are supported by DNA and I will list any physical features that also agree.

Supergroup Excavata (some members of this group have an “excavated” groove on one side of the body)

  • Diplomonads
  • Parabasalids
  • Euglenozoans

Supergroup SAR (This includes 3 major groups supported by DNA, Stramenopiles, Alveolates and Rhizarians) [many in this group are currently listed under the Kingdom Chromista]

Clade Stramenopiles (Several members of this clade have a large “hairy” flagellum accompanied by a smaller “smooth” flagellum)

  • Diatoms
  • Golden Algae
  • Brown Algae

Clade Alveolata (This group has a membrane-enclosed sac called an alveoli under the plasma membrane)

  • Dinoflagellates
  • Apicomplexans
  • Ciliates

Clade Rhizarians (many of the members of this clade are amoebas that have thin needle-like pseudopodia)

  • Radiolarians
  • Forameniferans
  • Cercozoans

Supergroup Archaeplastida (These are the plants and their “protist” relatives)
Red Algaes

  • Chlorophytes - green algaes
  • Charophytes - another group of green algaes that are more closely related to plants
  • Plants

Supergroup Unikonta (the clades in unikonta are supported by molecular studies but there is still a lot of debate about the organization within this grouping)

Clade Amoebozoans

  • Slime Molds
  • Tubulinids
  • Entamoebas

Clade Opisthokonts

  • Nucleariids
  • Fungi
  • Choanoflagellates
  • Animals

Here’s a nice article about the history of Kingdoms. It was written in 2011, so it’s only up through what we knew in 2011ish.

When I took Botany as an undergrad, our professor was of retirement age and he taught us there were two Kingdoms: plants and animals. if it was green, it was a plant, if it wasn’t green it was an animal! He was a few decades behind even back in 1988. Looks like your college class is about 10-15 years behind current knowledge also.

An interesting thing about Paramecium (and other ciliates)…they evolved from ancestors that contained a chloroplast. Once we deduced that, it instantly required their reclassification. That happened not long after this discovery in 2008: https://doi.org/10.1016/j.cub.2008.06.031


@hanly @psweet @cmeckerman @pfau_tarleton Thank you all for all the insight. I never knew protist was a messy group that was essentially unstable. I will definitely be looking forward to more advancements in science and the classification of these amazing organisms. Thank you I will definitely keep this is mind.

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