(via This sea slug can lose its head and regenerate new body in three weeks | Ars Technica)
…Unlike autotomy in other species, these two types of sea slugs do not seem to shed their bodies in response to predatory threats. The authors note that adult sea slugs don’t have that many natural predators, and given how long it took for the specimens to detach their heads from their bodies, it wouldn’t be a useful strategy to escape a predator anyway.
Based on the findings of their experiments, the authors suggest that the real function of this behavior is to expel parasites—at least in Elysia atroviridis. Similar function has also been observed in earthworms infected with a protozoan parasite. “Alternatively, but not mutually exclusive to this idea, autotomy by the sacoglossans may function to escape from being tangled in algae or to remove accumulated toxic chemicals,” the authors wrote…