Protozoa and Chromista
Protozoa and Chromista are two eukaryotic kingdoms that contain a wide variety of mostly microscopic or structurally simple organisms. Their classification has shifted repeatedly over the past century, and different taxonomic systems still draw the boundaries in different ways. For the purposes of this project, I follow a traditional Linnaean framework, using the same broad structure adopted by iNaturalist and the Catalogue of Life.
I have relatively few photographs that fall into these kingdoms compared with plants, fungi and animals, but they are included here for completeness and because they raise some of the more interesting questions around classification.
Kingdom Protozoa
Protozoa is a historical kingdom used for eukaryotic organisms that are not plants, animals or fungi, and that are usually single‑celled or simple in structure. Modern phylogenetics has shown that “protozoa” is not a natural evolutionary group, but the term remains useful in a practical, Linnaean sense for organising organisms that do not fit comfortably elsewhere.
In this project, Protozoa includes the phylum Mycetozoa (slime moulds). Their placement varies between systems, but grouping them here reflects their treatment in iNaturalist and several contemporary references.
Slime Moulds (Phylum Mycetozoa)
Slime moulds are among the most unusual organisms in the eukaryotic world. They are not fungi, despite their spore‑bearing fruiting bodies, and they are not animals or plants. Their life cycle includes amoeboid, mobile stages that behave almost like tiny animals, followed by a reproductive stage that resembles a fungus.
Historically, slime moulds have been placed in Protozoa, Fungi, or even their own separate kingdoms. Modern classifications generally treat them as amoebozoans, but their Linnaean rank varies depending on the system.
Most of my Protozoa records belong to this group. Many are yet to be identified reflecting both the complexity of slime mould taxonomy and the limitations of photographic identification.
→ Phylum Mycetozoa (Slime Moulds)
Kingdom Chromista
Chromista is a diverse kingdom that includes organisms previously assigned to Protozoa, Plantae or Fungi. Members of this kingdom include:
- Brown algae (Phaeophyceae)
- Diatoms (Bacillariophyta)
- Golden algae
- Oomycetes (water moulds)
- Various other groups of algae and protists
Chromists are especially important in marine and freshwater ecosystems, where they contribute significantly to global photosynthesis and nutrient cycling.
At present, I do not have photographs that clearly fall within this kingdom, but it is included here to maintain a complete classification structure.
Notes on classification
The organisation of Protozoa and Chromista varies widely between taxonomic systems. This project uses a traditional kingdom–phylum–class structure because it is intuitive and works well for organising photographs. Where sources differ, I generally follow the practical approach used by iNaturalist and the Catalogue of Life, while recognising that alternative arrangements exist.