Kwinana Rockingham Mandurah Branch, 22 September2025
The presentation for the September Meeting was on the Protozoa, and speaker Daniel Heald provided this summary report.
Guest Speaker and member Daniel Heald discussed creatures quite a bit smaller (most of the time) than his usual insects, including their phenomenal diversity, intricate structure, and complex interactions with each other and intercontinental events.
In the centuries since Antoni van Leeuwenhoek discovered microorganisms in 1674, it became increasingly clear that the microscopic world is even more complicated than the macroscopic one, to the point that a random sample can contain creatures so different to anything else that it’s like discovering mammals for the first time—or even vertebrates as a whole. Every animal and plant you’ve ever heard of is a tiny fraction of the diversity of the ones that never evolved multicellularity.
The size range of single-celled eukaryotes is also phenomenal – from Picomonas judraskeda (first discovered as DNA in Arctic seawater) at three millionths of a meter long, to the Xenophyophores of the deep sea, which can be up to 20cm across. Even well-known protozoa such as the common Amoeba and Paramecium can be larger than the smallest insects.
Their genetic relationships are also surprising, even considering their origins as bacteria, cyanobacteria, and archaea that engulfed each other to become entirely new organisms with specialised organelles such as nuclei, mitochondria, and chloroplasts. ‘Water Moulds’, for example, are not fungi, but red algae that picked up fungal genes from somewhere.
One notorious member of that group is Phytophthora dieback, which is more closely related to giant kelp than kelp is related to other multicellular plants. Another infamous Phytophthora is P. infestans, which wiped out the Irish potato crops in the mid-1800s and caused the Irish diaspora.
Daniel also discussed specialist predators among the protozoa, and the sophisticated internal structure of many, the eyespot of Euglena, and the mechanical computer that Euplotes uses to coordinate its leg-like cirri.
Less well-known species were also discussed – the Slime Nets of the Labyrinthulomycetes, which are normally harmless decomposers, even capable of digesting pollen, but which wiped out every marine seagrass colony of the North Atlantic in the 1930s, causing the extinction of species like the Eelgrass Limpet Lottia alveus.
Some parasitic protozoans were mentioned, including malaria and the deadly Brain-eating Amoeba. Dinoflagellates such as the horrifically toxic Karenia mikimotoi, currently poisoning the ocean in South Australia, and Noctiluca scintillans that can glow a brilliant blue, were featured.
Daniel closed by covering some of the shelled amoebas known as Foraminifera, one of which was the subject of his Honours thesis decades ago. When originally discovered, one biologist thought they were microscopic octopi. Other forams build star-shaped homes that make up most of the ‘sand’ on beaches in Tuvalu and elsewhere. Their intricate shells are abundant in the fossil record. The Pyramids, for example, contain millions of fossil Nummulites in their limestone blocks. And Gromia sphaerica, up to 3cm across, rolls around on the deep-sea ooze and leaves tracks identical to some in 1.8-billion-year-old rocks.
Daniel Heald