Crabs and Shrimps often form commensalistic symbiotic relationships with anemones in tropical waters, again for the purposes of protection from predation. For instance the Anemone crab, Neopetrolisthes oshimai, which is a filter feeding Porcelain crab, lives and captures its food from within the tentacles of giant anemones.
While diving in Papua New Guinea we have been fortunate enough to see several interesting commensalistic relationships. Apart from the Anemone crabs, we have also filmed Imperial shrimps, Periclimenes imperator, hitching a ride on the large sea cucumbers found here, (genera Stichopus). The shrimps get transported through a large area of potential food by their host with only a minimal expenditure of energy on their part. They can be observed getting off their host cucumber to feed in productive areas, and back on for a ride to the next spot! The Imperial shrimp also rides on large nudibranchs such as genus Dendrodoris, which although slow moving, afford the shrimp with protection by virtue of their toxic chemical secretions and warning colouration. Although this is currently classed as a commensalistic relationship, it is possible that the Emperor shrimp may assist the nudibranch by removing parasites.