If you're a unicellular organism, chances are you might want motility at some point or another. Being able to move helps escape predators, find food, find better sunlight access if you're photosynthetic, find a partner for some nice quick steamy sex; as well as entertaining easily-amused cell biologists.
Cell motility tends to fall into two (crudely-defined) broad categories:
1. Amoeboid -- cell extends pseudopodia ("false feet") and pulls itself into a particular direction along a surface.
2. Flagellate -- cell uses whip-like flagella to propell itself through a fluid. The flagella can be short and numerous, as in the cillia of a Paramecium, or long and few in number. You'd expect the flagellum to originate in the back of the cell, pushing it forward. Our sperm do that. However, interestingly enough, the majority of eukaryotic life voted against posterior flagella. Animals and their closest relatives, fungi, form a group called opisthokonts -- Greek for "posterior tail". Almost every other eukaryotic organism has anterior flagella -- and at least a couple of them. We're just weird.
There's also adhesive-based motility, where the cell is like a rock climber -- it anchors itself to the surface, uses cytoskeletal motors to move ahead, and then abandons the anchor. Diatoms and the malarial parasite use such technique.
However, there's something even weirder. (this is Protista -- there ALWAYS is something weirder!)
Imagine you're floating around in fluid, and you just can't be bothered to whip things around on the outside. Nor do you feel like protruding pseudopodia along a surface, like some lowly amoeba. Nor do you want to associate yourself with the brown algae because you're racist like that. Or rather, imagine that evolution does weird things. It really does...
What would you do?
This creature decided it wants to be a snake-in-a-bag:
Meet Saccinobaculus, an anaerobic resident of the gut of the wood-eating cockroach Cryptocercus. The stiking feature in the middle is the axostyle -- a think bundle of microtubules (cytoskeletal structural elements) that functions in a similar way to the muscle tissue... of a snake in a bag, which is what the name really means! This axostyle is highly motile and wriggles around inside the cell, causing it to move. This seems to be a rather inefficient mode of motility, but the creature hasn't gone extinct yet, so it can't be that bad.
But you have to see it in action:
I searched all over the internet for a movie of a Saccinobaculus moving about. Unfortunately, I failed to find any. Either my search skills suck or there just isn't any publically available out there yet. So I'll have to make do with a crappy clip I shot in class. Appologies for the shitty quality, and half-deteriorated specimen. As soon as I have legitimate access to a professional scope with a decent camera, and acceptable specimens, I'd try to fix this...
So next time you catch a harmless snake and throw it in a plastic bag, for whatever awkwardly surreal reason, be sure to remember that there's an organism that moves like that for a living. And please don't hurt the snake -- they're beautiful animals!
This advice is serious: If you have access to a microscope, and some wood-eating roaches, or Zootermopsis termites nearby, please remove the gut of one and examine it under the microscope. You'll be amazed by what you find! Unfortunately, the organisms tend to die quickly upon contact with air, so you can't really culture them for your enjoyment...