Sometimes Imperial shrimp will ride on other animals like nudibranchs, and these animals offer protection to the shrimp because they are poisonous to other animals. Several species of sea cucumbers host the Pearlfish inside their intestines during the day. At night, the Pearlfish swims out of the anus of the sea cucumber to eat crustaceans. The sea cucumber doesn't seem to mind this odd guest and the Pearlfish is relatively safe during the day.