This hermit crab was just minding its own business when it got picked up by a sea urchin's tube feet. What follows is an awkward fight between two creatures for which maneuverability isn't a strong suit.
The sped-up footage lends a look of desperation to this crab's struggle. The crab isn't in too much danger. Although sea urchins will occasionally eat mussels or barnacles, they aren't really equipped for stuff that can move out of reach.
If you're wondering how a sea urchin eats, it uses five plates that come together like a beak. Just to add a bit of poetry to the awkward grapple, the structure that the urchin uses to eat is called "Aristotle's lantern." That sounds a lot nicer than "mouth," doesn't it? These plates scrape algae and other bits of food off of rocks and discarded shells. The urchin probably picked up the befuddled crab in the first place looking for the microbial life that lived on its shell.