The most widely studied group of decorators are crabs of the superfamily Majoidea. The group has over 900 species, about 75% of which show decorating over some or all of their body, having specialized hooked setae to attach material from the environment. Wicksten documented carrying behavior in at least four families of brachyuran crabs. This involves shorter fifth and sometimes fourth legs that are no longer used for locomotion but to lift an object (e.g. a shell, piece of sponge or coal, or rock) over the dorsal aspect of the posterior part of the carapace. Ross demonstrated in the laboratory that octopus failed in attacks on hermit crabs carrying a sea anemone on their shell, with previous work demonstrating that the crabs actively transfer anemones onto themselves. Numerous species of sea urchins and gastropods of the family Xenophoridae cover themselves with small rocks, shells and algal fragments. Some cover themselves for days or weeks at a time, others for only a few hours.