Wouldn't this make them a massive vector for prion disease if it established in their tissues? I don't mean in a homocentric fashion, you'd expect to see prion borne diseases in their predators.
Lucky then that we're not eating their innards. Oh wait.
The problem with prions are cycles. If sea urchins use to eat other sea urchins once a prion is formed it can multiplícate and accumulate in the sea urchin that eat them. Lucky, they eat algae.