Blue is an unusual color for a sea star, but the species that forms the background in this photo, Linkia laevigata, is one of the most conspicuous inhabitants of South Pacific tropical reefs. It has thin arms, about the diameter of a cigar, and a rather stiff skeleton, making it rather hard and innflexible. These characteristics are important in defense, but it also contains chemicals in its tissues that are poison to predators.

Despite its poisoned skin, Linkia is home to at least two surface parasites, or ectoparasites. One (shown here) is a type of limpet. The limpet matches its color perfectly to the sea star color by borrowing pigments from its host.