But how do you change the āGhostsā from āthings that kill youā to āthings you can kill?ā
Iām not sure if this was just for fun, but itās a fascinating way to demonstrate how spatial structure alters predator-prey population dynamics.
First, cut your hair funny.
Then put a spike in a bagā¦
Would have been more impressed with Q*bert.
Rotifera: What do you suppose God is like?
Predatory Bacteria: I believe God is a wise benevolent Creator who made this world so I could eat you.
Euglena: That seems awfully convenient for you.
Predatory Bacteria: Come here, you tasty heretic.
I agree that āwise benevolent creatorā seems a bit too neat; but can you think of any theologians cool enough to postulate ā80ās retrogaming nostalgia microfluidics overlordā when asked about the probable nature of god? That one would be tricky except by revelation.
Iām half convinced that at this point the alien programmers running our simulation are just messing with us before they fdisk.
That would be a pretty damn big predatory bacterium to eat either a Euglena (~40 microns long) or a rotifer (~50 microns). Bacteria are typically about a micron across.
God, the wise benevolent Creator, made me huge.
Related:
"Oh,grandmotherbacterium, what a horribly big mouth you have!" - "All the better to eat you with!" And with that he jumped out of bed, jumped on top of poorLittle Red Riding HoodEuglena, and ate her up.
Very good! Or Centipede, although that might be too obvious 
No biologist here, but there are these fellas. Maybe snack would be a better word?
Amen, Sibling!
They only attack other bacteria. Think of prokaryotes (bacteria and archaea) as flies, single celled eukaryotes (protists) as cats, and tiny multicellular eukaryotes (rotifers, tardigrades) as bears. Itās simplistic but helpful!
So there are lots of flies that eat other flies and some that parasitize each otherā¦and there will also be bunches that treat bigger things (cats and bears) as terrain (like botflies).
And there are some cats that are bigger than bears (Tigers vs. Sun Bears), but bears are bigger than most cats.
Err, and there are cats and bears that filter feed on flies en masse in this scenario, which kind of doesnāt work, but itās a fun mental image!
True, although they are still small and are sucking the cytoplasma from other bacteria. And the Bdellovibrio/Bacteriovorax types which Iāve worked on. They are more like Alien chestbursters than predators in a normal sense, as they replicate within a cell and then burst it open rather like some viruses.
Neat! Iām going to have to drain your brain at some point. Iām a huge tiny-life-made-of-molecular-machines nerd (blame the folks at Small Things Considered, that āLife in a Phage Worldā book they put together completely blew my mind!)
That needs to happen! Centipede with a real centipede!
Anybody know of any protozoans with good ranged attacks?
Closest I can think of is Lacrymaria Olor with their absurd reach.
There are also a bunch of guys with extrusomes like Dileptus, but theyāve got really short range.
Iād be delighted by an ingeniously evolved counterexample; but my (admittedly very, very, rudimentary) knowledge of fluid mechanics makes me suspect that āranged attacksā probably arenāt really a concept at protozoan scales.
Youād definitely want someone who actually knows what they are talking about to discuss Reynoldās Numbers and similar(which I am not); but the punchline for small organisms is that the viscosity of the fluid you are working in is much, much, more influential than it is at larger scales.
You can see this with suspended dust and sediment in water and air: the drag of the fluid is sufficient to counter-act gravity(if thereās even a slight breeze/current available) and despite being denser than the surrounding fluid the particles just Brownian-motion merrily around more or less indefinitely rather than settling out.
Thatās not good news if you want ranged weapons to work: kinetic projectile weapons will have pitiful inertia compared to the effect of drag, so even if you could launch them at heroic velocities theyād still be aimlessly drifting after a very short flight. If you use toxins or viruses or something you can at least avoid the need to have enough kinetic energy when you arrive at the target to cause damage; but you still need to arrive.
Spraying venom or other noxious secretions at your enemies is also tricky(especially underwater, since unlike in air the fluid you are spraying is unlikely to be much denser than water or take advantage of surface tension since it is probably water based). Microorganisms certainly diffuse toxins at one another all the time; and it works quite well; but itās not a strategy for the impatient; and itās more of a concentration gradient than a spray attack.
You pretty much just have to reach out and engulf someone if you want to have an effect.
That was kind of my expectation. (with an allowance for extrusomes, of course)
I donāt know of any protozoans (I am admittedly an amateur) that has anything āprojectile-ierā than extrusomes, which are just a pneumatocyst analogue that is a part of a cell instead of an entire one (same idea though, little skinny quick-shooting stabby things) 
