The crab above is mainly decorated for camouflage but has moved onto a black sponge. The crab below has decorated himself with a sponge which is highly toxic.  This is known as Aposematism. The poisonous sponge signals to predators that the prey is toxic. This signal is beneficial to both the prey and the predator. It protects the prey and tells the predator that the prey is toxic thereby protecting it as well. Decorator Crab belonging to the superfamily Majoidea

Decorator Crab- Facts and Photographs

Decorator crabs belong to the superfamily Majoidea and are also commonly known as Spider Crabs.  They obtain their name from their habit of decorating their bodies with various plants and animals. This can ...