The single celled eucaryotes truly are a fascinating group to me, they’ve managed to diversify themselves massively considering their likely historic origin. (though their diversification pales in comparison to the procaryotes) still, they often-times seem much more complex with much larger genomes and usually cell size as well, with being up to 10 times as big in a linear fashion and somtimes having up to 1000times the volume.
but anyway, you have your hunters the protozoa who can often-times zip around before finding/attacking another cell, and then engulfing it through phagocytosis one of my favorite examples is Didinium, its part of the ciliates, it has two rings of cilia around its body, that it waves or moves (whatever) to propel itself through the water, when it finds its prey, little paralysing darts come out of the cells ‘snout region’ (an area that looks like a snout) and it uses them effectively on the other cell its hunting.
This is also the lifestyle suggested for the common ancestor of all eucaryotic cells, a hunting cell which would have needed a nucleus to prevent dna damage from the cytoskeleton as it moved around, perhaps attempting to engulf other small cells, and so, eventually, about 1.5 billion years ago, an ancient eucaryotic cell or precursor to true eucaryotic cells, engulfed some bacteria it couldn’t properly digest and a symbiosis was eventually born, evetually those bacteria ended up evolved structures of cells, the mitochondria. Mitochondria still have their own circular dna, some of their own RNA’s and ribosome, their genomes also look like cut down versions of the corresponding bacteria, with some of that cut down genetic information someone migrating itself over into the larger genome of the overall organism over evolutionary time.
This also applies to the photosynthisizers(sp) even though they have a cytoskeleton they have essentially lost their ability to move around and hunt, instead evolving thickening cell walls and turning from hunting into farmers. after ancient mitochondria based eucaryotic cells engulfed another, different bacteria.
Then we have the fungi and some other cells, they effectively have mitochondria but can’t engage in the hunting methods of the protozoa, they essentially scavenge off the secretions of cell workings or cell death.
The protists are a spectacular group, I imagine they’re hard to study due to their small size and massive genomes, but looking at some members of the group of protozoa, one find some amazing predatory cells.