If you are looking at the ladybird (ladybug) with the amoeba to the left, the amoeba isn't an order of the magnitude smaller - it would actually be visible by the human eye (bigger than a grain of sand)? Indeed, the amoeba seems the same size as the ladybird's foot?
Similarly, this makes the bumblebee appear smaller than a human finger (the in the adjacent picture), which isn't the case?
Only the next row above it, with Pelomyxa, is indeed an amoeba and one that is very frequently encountered and which usually has sizes not much less than 1 millimeter and sometimes it can reach a size of a few mm.
The true amoebas are much more closely related to humans, than to xenophyophores (giant marine unicellular living beings) or to plants.
Besides the true amoebas there are also a few other kinds of unicellular eukaryotes with shape-shifting cells, e.g. foraminifera, radiolarians and others, but already in the first half of the 19th century it was recognized that those other groups change their shapes in a different way than the amoebas, so they were classified separately, even if the term "amoeboid cell" has always been used about any cell with variable shape.
The true amoebas are related to the group formed by animals and fungi, and there are some amoebas that have a simple form of multicellularity, so it is likely that some of the mechanisms needed for the evolution of multicellularity have been inherited from a common ancestor of animals, fungi and amoebae.
The multicellular or multinucleate amoebae that belong to Myxomycetes (one of the kinds of slime moulds) can reach much bigger sizes, e.g. a diameter of up to 1 meter, because they do not have the size limitation that exists for simple unicellular eukaryotes.
Most tardigrades are not much bigger than 100 micrometers.
Tardigrades, together with nematodes, rotifers, mites and a few more rarely encountered groups are among the smallest animals and they are smaller than many of the bigger among the unicellular eukaryotes. That is why they have been discovered only after the invention of the microscope.
The tardigrades have evolved towards smaller and smaller sizes very early, already during the Cambrian. It is interesting that they are segmented animals, like their relatives the arthropods and the velvet worms, but they have very few segments, because in order to achieve such a small size they have lost all intermediate segments, so the segments that now form their body were originally the segments of the head, and now they are followed immediately by the original segments of the tail, without the original body that connected the head to the tail. Thus they have been miniaturized by losing their body and becoming a walking head (the legs of the tardigrades are what in arthropods have become appendages of the mouth, e.g. mandibles and maxillae).
"Megaphragma mymaripenne is a microscopically sized wasp. At 200 μm in length, it is the third-smallest extant insect, comparable in size to single-celled organisms. It has a highly reduced nervous system, containing only 7400 neurons, several orders of magnitude fewer than in larger insects."
I'd suggest keeping the SI unit , or at least having both once we get to the level of inches.
Even with setting it to metric, it progresses through units based on the scale. I realize that scientists love to work in scientific notation, and progressing from nanometers to micrometers, mm, cm, and finally meters sort of follows that kind of logic. I wonder how it would feel if the whole thing was in constant units or at least there was an option for that.
I never knew about these either.
> Eutelic organisms have a fixed number of somatic cells when they reach maturity, the exact number being relatively constant for any one species. This phenomenon is also referred to as cell constancy. Development proceeds by cell division until maturity; further growth occurs via cell enlargement only.