I try not to anthropomorphize my critters, to remember that they have their own lives that don't necessarily mesh with ours. But sometimes the temptation is strong. I know the face on that poor victim is just a fluke of camera angles; she* doesn't really have a down-turned mouth and a pug nose. She's not really going to be forced to hand over her lunch money. It just looks that way.
But some things are almost universal, among humans, animals, and even plants: the struggle for place, for food, for sex or its equivalent. And these skeleton shrimp are fighters; they cross paths often, and when they do, they hit and bite at each other. Usually it ends quickly, as the smaller one backs away.
|A few seconds later; fight ended, all is forgiven and forgotten.|
These tiny beasties are usually standing upright on swaying seaweeds. Nothing seems to dislodge them, even when I pick up a handful of algae and swish it around in the water to shake out any muck or unsuspected hitchhikers. When I drop the algae back in the tank, there are all the skeleton shrimp, standing tall, as if nothing had happened.
When they move from one branch of seaweed to another, or travel down a blade of eelgrass, they bend over, grasp the path ahead with their big, hooked "hands" (gnathopods), then bring up the back legs, the way an inchworm moves. But as soon as they've reached their destination, they stand up again.
Those six prehensile legs explain how they maintain their footing.
*She's carrying young; see her swollen brood pouch? The larger one is probably a male.